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A Cross-sectional Triangulation Analysis of the Knowledge, Attitudes and Practices of Patients from the Endocrinology Clinic of the Philippine General Hospital on the Use of Herbal Dietary Supplements
Scott Riley K. Ong, Jana Deborah B. Mier, Bryan Vincent Q. Mesina,
Karen Anjela M. Montevirgen, Maria Isabel P. Nabor, Lovely Angelica A. Nagpala, Ana Louise M. Naidas,
Marianne Joy N. Naria, Zane Oliver M. Nelson III, Ericka Joan R. Nera, Maetrix O. Ocon,
Janna Elyza P. Olivera, Kimberly Mae C. Ong, Patricia C. Orduña, Abigail Z. Ortal, Alexandra P. Pacheco,
Ronnellee G. Paclibar, Sarah May C. Padre, Hanna Francesca M. Palomar, Susie O. Sio and
Ma. Concepcion C. Sison
Department of Pharmacology and Toxicology. College of Medicine,
University of the Philippines Manila
Herbal dietary supplements (HDS) have rapidly gained popularity among consumers in the recent years. According to Sia,1 the Bureau of Food and Drugs, now known as Food and Drug Administration (FDA), reported that a total of 5 billion pesos was earned by the companies of the top 7 selling brands of dietary supplements in the country in 2007. In 2010, it was reported that Filipinos were spending more than 75 billion pesos a year on dietary supplements. This is on top of warnings from the Department of Health that people “do not really need these food supplements for health and well-being” and that they may even have “harmful side-effects.”2
In the Dietary Supplement Health and Education Act (DSHEA) of 1994, enacted by the US Congress, a dietary supplement was defined as “a product (other than tobacco) intended to supplement the diet that bears or contains one or more of the following dietary ingredients: (A) a vitamin; (B) a mineral; (C) an herb or other botanical; (D) an amino acid; (E) a dietary substance used by man to supplement the diet by increasing the total dietary intake; or (F) a concentrate, metabolite, constituent, extract or combination of any ingredient described in clause (A), (B), (C), (D) or (E).”3
HDS constitute the type of dietary supplements that are derived from plants or plant parts. A typical consumer may use HDS for various reasons. It has been reported that some use them as treatment for various illnesses. In certain cases, they are even used as alternatives to conventional drugs in the belief that they do not cause the side effects associated with the latter.4 However, it must be emphasized that these products have not undergone stringent clinical trials on their efficacy and safety and cannot be used as replacement for drugs.5 Though claimed to have health benefits, HDS may not necessarily have therapeutic value.2
In March 2010, the Department of Health issued Administrative Order 2010-0008, which directed the replacement of the label "No Approved Therapeutic Claims" with its Filipino translation, "Mahalagang Paalala: Ang (name of product) ay hindi gamot at hindi dapat gamiting panggamot sa anumang uri ng sakit," in any form of advertisement, promotion or marketing of dietary supplements.6 However, just nearly three months after its issuance, the implementation of the said administrative order was suspended by means of a writ of preliminary injunction issued by the Manila Regional Trial Court, following a court action filed by the Chamber of Herbal Industries of the Philippines, Inc.7
Here in the Philippines, studies on the use of HDS have been very limited. This study was thus intended to address this issue. It aimed to determine the knowledge, attitudes and practices (KAP) of patients on HDS. Specifically, this study aimed: (1) to determine the perceptions of patients on the perceived therapeutic value of HDS; (2) to determine their perceptions on the safety of HDS; (3) to identify the reasons for their use or non-use of HDS; and (4) to identify the presence of any associations among the preceding three variables. By providing further knowledge on the KAP of patients on HDS, this study can aid physicians in understanding their patients’ attitudes toward HDS and prove useful in improving patient management and the physician-patient relationship.
This study was limited to patients from the endocrinology clinic of the Outpatient Department of the Philippine General Hospital. It intended to provide baseline data on the KAP toward HDS of the said population. In this study, judicious use of HDS was considered as that involving awareness of the difference between HDS and conventional drugs and the lack of established evidence on the therapeutic value and safety of HDS.
Materials and Methods
This study utilized methodological triangulation involving three methods of data collection, namely, survey, in-depth interview, and focus group discussion (FGD). These methods were used to cross-check information obtained regarding HDS KAP.
This study was performed on patients consulting at the endocrinology clinic of the Outpatient Department (OPD) of the Philippine General Hospital (PGH) on September and October 2010. Patients eligible for the study were anyone above the age of 18 years, regardless of reason for consult, sex, socioeconomic status, and educational attainment. Patients excluded from the study included those who were 18 years or younger and those who were unable to understand and speak the Filipino language.
The survey was performed on a sample size of 175 patients, selected through convenience sampling (α=0.05, P=0.50, t=1.96). In-depth interviews were performed on 5 HDS users and 4 non-HDS users, and FGD was performed on 2 groups of 6 and 7 participants. For both interviews and FGD, sample sizes were determined using the grounded theory approach and participants were selected through purposive sampling.
Method 1: Survey
Purpose. The survey was used as a quantitative method to measure the knowledge and attitude components of the study, as well as to address basic questions on the usage of HDS.
Tool. The survey questionnaire was composed of questions that addressed the respondents’ (1) knowledge on the therapeutic value and safety of HDS, as well as (2) their attitudes regarding the perceived therapeutic value, safety, and affordability of HDS. Knowledge items were answered as true, false or uncertain, while attitude items were answered using a five-level Likert scale. A few questions on the use or non-use of HDS by the respondents and their understanding of the label “No Approved Therapeutic Claims” were also included. The survey was administered by trained survey supervisors.
Pretesting. The questionnaire underwent pretesting with a sample size of 16 patients. Cronbach’s alpha reliability coefficients of 0.912, 0.774, and 0.849 were obtained for attitude items on therapeutic value, safety, and affordability, respectively. The minimum factor loading of 0.5 for validity, as suggested by Costello and Osborne,8 was satisfied by all attitude items. Knowledge items did not undergo testing for reliability and validity since they were simply meant to determine the respondents’ ability to answer them correctly.
Data Analysis. Data was encoded and analyzed using the software Statistical Package for the Social Sciences (SPSS), with alpha level set at 0.05. Statistical tests, such as Chi square, Spearman’s rank correlation and Cramer’s V, were performed.
Method 2: In-depth Interview
Purpose. The in-depth interview addressed the practice component of the study, delving deeper to understand the contexts of such practices and to explore the motivations behind them, as well as to relate them with knowledge and attitudes toward HDS.
Tool. The interview guides were composed of open- ended questions addressing (1) general data on the patient, (2) perceived quality of life, (3) state of health and illnesses, (4) perceived therapeutic value and safety of HDS, and (5) attitudes and practices on HDS (Table 1). The interviews were conducted by trained interviewers.
Table 1. Outline of interview guide
Data Analysis. Audio recordings of the interviews were transcribed verbatim. Data was analyzed using the constant comparison method. Data was coded into categories and emerging themes within and between categories were identified.
Method 3: Focus Group Discussion
Purpose. The FGD further explored the attitude and practice components of the study based on the collective experiences of the study subjects on HDS use or non-use.
Tool. The FGD guide included (1) a comparison between HDS and conventional drugs, (2) the purpose and effect of HDS, and (3) experiences on its use or non-use (Table 2). The discussions were moderated by trained facilitators.
Data Analysis. Data analysis was performed in the same manner as the interviews, the process of which was discussed in the preceding section
Table 2. Outline of focus group discussion (FGD) guide
The themes that emerged from the in-depth interviews were compared and analyzed together with the themes that resulted from the FGD. The findings from these two qualitative methods were then analyzed in conjunction with the findings of the survey. Such integrated analysis of data from all three methods led to the construction of a conceptual framework on the KAP of both HDS users and non-users.
This study was approved by the Technical Review Board and the Ethical Review Board of the Research Implementation and Development Office, College of Medicine, University of the Philippines Manila. Participation in the study was voluntary. All participants were informed regarding the nature of the study and were required to sign an informed consent document. Their identities and right to privacy were respected.
The demographic data of the sample population used in the survey are shown in Table 3. Most of the respondents (69.7%) were from ages 31 to 60 years, with the 41-50 age group having the most number (26.3%). Majority were female (78.9%) and unemployed (78.9%). The National Capital Region (NCR) was the most common place of origin among the respondents (40.6%). Half had secondary education as their highest educational attainment (49.1%). No statistical relationships were found between usage of HDS and any of the demographic variables (p>0.05).
Table 3. Demographic data of the study population involved in the survey
Knowledge. The respondents’ source of information on HDS was mainly media advertisements (85.7%). Other important sources of information were friends (32.0%) and family (29.1%). Their responses to the knowledge items of the survey are summarized in Table 4. Among the items, only one (KT1: HDS as treatment for diseases) showed no significant difference in the participants’ responses (p>0.05). Most had incorrect ideas about the perceived health benefits of HDS. FDA approval was incorrectly associated with the presence of perceived health benefits of HDS (KT4).
Table 4. Frequency analysis of survey items for knowledge on herbal dietary supplements.
However, majority (52.0%) still thought that there is a difference between HDS and prescribed medications in terms of perceived health benefits (KT2). Knowledge on the safety of HDS was varied. Some believed that HDS may have harmful side effects, while others believed that they are safe to use. In general, most (94.9%) agreed that extensive testing and evaluation is necessary to assure safety of an HDS product. However, most (54.9%) also believed that HDS have gone through such evaluation.
Understanding of the label “No Approved Therapeutic Claims” was rather poor. Only 24.0% of the respondents understood it correctly. None of the demographic variables, including educational attainment and income, showed significant associations with the respondents’ understanding of the label (p>0.05).
Attitudes. The responses to the attitude items of the survey are summarized in Table 5. All items showed significant differences in the participants’ responses (p<0.05). Most respondents generally agreed to the perceived health benefits of HDS, whether for disease prevention (64.0%, AT2), slowing down its progression (61.1%, AT7) or providing symptomatic relief (66.9%, AT9). A smaller percentage (46.9%) believed that HDS are effective in treating diseases (AT14). Nevertheless, a considerable percentage (35.4%) believed that HDS have no therapeutic value in the treatment of diseases. Most (75.4%) believed that conventional medicines prescribed by physicians are more efficacious than HDS (AT4). Attitude items on the safety of HDS revealed the belief of majority (53.2%) that there may be harm with excessive intake of HDS (AS1). Furthermore, majority (Table 5) felt the need to consult one’s physician about the use of HDS (AS8, ATS1, ATS2) and the insufficiency of information provided by manufacturers regarding the safety of their products (AS9). Attitude toward the affordability of HDS was varied.
Practice. Most respondents (89.7%) were under conventional medication and only 22.3% were HDS users. HDS use did not show significant association with one’s understanding of the label “No Approved Therapeutic Claims” (p>0.05).
Perceptions on Health. Health was considered by many participants as an important determinant of their quality of life. They viewed being healthy as a positive condition that is affected by physical, mental, and economic factors. Some pointed out that health is not just the absence of disease but also the stability of the body and mind. Efforts exerted by the interviewees to achieve good health included intake of medicines, having a balanced diet, regular exercise, and avoidance of vices. For some, being healthy also involves having the proper mind set regarding their illnesses.
Perceptions on Illnesses. HDS users had different views regarding their illnesses. Two of them claimed that illnesses arise from intake of unhealthy foods. Others believed that illnesses are an inevitable part of life. There were those who expressed acceptance of their illnesses and hopelessness for cure. In contrast, non-HDS users were observed to view their illnesses as mild and less serious. It was observed that the participants’ health behavior reflects their personal view of health and their illnesses.
Knowledge. Majority of the participants had a basic level of awareness on what an HDS is. Reported indications for HDS include strengthening of the body, cleansing of the body from toxins, preventing disease progression, and treatment of specific diseases, such as hypertension, dyslipidemia, and cancer.
Table 5. Frequency analysis of survey items for attitude toward herbal dietary supplements
Knowledge on the role of the FDA in regulating HDS was poor. A few reported that FDA approval of an HDS entails its safety and lack of side effects. Understanding of the label “No Approved Therapeutic Claims” was varied. Those who were aware of it understood it in terms of their knowledge about drug regulation or their perception of health benefits from HDS. Many agreed that the label indicates that HDS should not be used in the treatment of diseases although they may help in maintaining health and providing some relief from illnesses. One user reported lack of understanding due to the label being written in English instead of the native language Filipino.
Attitudes. All users had the notion that HDS are beneficial to their health. Some regarded them as food supplements that are safe and have no side effects. The notion that they are “herbal” and “natural” was associated with being safe for use. Non-users recognized HDS as natural and thus argued that they are generally good for the body. However, they were regarded as different from conventional drugs and not to be used to treat diseases.
Practice. All interviewed users reported continued intake of prescribed conventional drugs along with HDS, albeit usually at a different time of the day. However, they expressed their prioritization for prescribed conventional drugs over HDS. They considered HDS as mere supplements and thus not to be used as alternatives to conventional drugs. Family emerged as an important factor. Some were just convinced by their relatives to use HDS, while others used them as means of exhausting all possible ways to make themselves healthy for the sake of their families. Accommodative surface values such as hiya and pakikisama also emerged as important factors.
Users generally agreed that HDS are costly. Despite this, they reported continued use of the product on top of their prescribed medications. However, when asked if they would recommend the use of HDS to others, they expressed hesitancy in doing so. Additionally, only two out of five interviewees reported disclosing their use of HDS to their physicians. One reported non-disclosure due to the fear of getting reprimanded by her physician. Another felt that her use of HDS was irrelevant to her medical therapy and considered it as “no big deal”.
Among non-users, priority for physician-prescribed drugs and the costliness of HDS were reasons for non-use. The opinions of their physicians were also important. Most refused to use any HDS without consulting their physicians first. Nevertheless, many expressed willingness to try them if given the opportunity due to the perception that they are generally safe and the positive experiences of others on HDS use.
Focus Group Discussion
Knowledge. The differences between conventional drugs and HDS were recognized by many participants. They agreed that the former have undergone extensive studies to prove their therapeutic effect while the latter may have not yet undergone full evaluation. Some pointed out that conventional drugs have defined chemical composition and require specific dosage regimens for intake. In contrast, HDS may not have defined compositions and do not require strict adherence to a specific dosage. HDS were perceived as natural products, and as such they were regarded as generally safe, even with excessive and prolonged intake. However, a few thought that HDS and conventional drugs are the same. For them, both are used for treatment of diseases.
Understanding of the label “No Approved Therapeutic Claims” was varied. Some pointed out that this label bears no recommendations for consumers to use the product. It was further added that seeing it should serve as warning to buyers to not expect any therapeutic benefits from the product. Others associated the label with safeness for use.
Attitudes. Perceptions on the health benefits of HDS were varied. Some believed that they are effective in treating diseases, while others claimed that they are not really effective for such purpose or that they serve as mere supplements to conventional drugs. However, it is noteworthy that the participants agreed that HDS have no side effects although taking them together with conventional drugs may result in certain interactions and unexpected adverse reactions. Nevertheless, they also agreed that intake of prescribed conventional drugs should always be prioritized over HDS use and that physicians must first be consulted before using any HDS.
Practice. Experience emerged as an important factor for the participants’ attitudes and practice on HDS use. It was noted that positive personal experience contributes to further HDS use. Furthermore, testimonials on the benefits of HDS, usually seen in media or heard from friends, are effective in promoting HDS use. In contrast, accurate knowledge on the nature of HDS, the scientific studies they have undergone and their regulation by FDA promote a more judicious use of HDS.
This study generally showed that the sample population is aware of what HDS are. The participants were able to identify them as distinct from conventional drugs. Survey results showed that a larger fraction of the population (52.0%, p<0.05) believed that HDS are indeed different from conventional drugs. However, there was still confusion as to which aspects make them different from the latter. The interview participants reported different purposes for HDS. Some were rather general, such as for strengthening the body, for increasing one’s stamina or for detoxification; some were more specific, such as for improving bowel movement, for decreasing blood cholesterol levels or for treating cancer. FGDs showed that there were those who regarded HDS as mere supplements to one’s medications and there were those who believed that they serve the same purpose as conventional drugs—that is, to treat diseases. Nevertheless, as the survey showed, those who considered HDS to be different from conventional medicines were the ones likely to believe that they cannot be used for the treatment of diseases (Cramer’s V=0.285, p<0.05) and thus cannot be used as alternatives to prescription drugs (Cramer’s V=0.266, p<0.05). On the other hand, those who claimed HDS to have the same purpose as conventional drugs were the ones likely to believe that they can be used as alternatives for such.
Knowledge on the role of the FDA in regulating the sale and availability of HDS in the market was poor, as all three methods have shown. While the participants generally believed that HDS must undergo extensive evaluation and clinical testing first before being made available for public consumption, they differed in their knowledge as to whether this really happens or not. The survey showed that a larger percentage of the population (54.9%, p<0.05) erroneously believed that HDS available on the market have actually undergone rigorous scientific evaluation. Furthermore, FGDs revealed that FDA approval of HDS affected the way people think about HDS. Such approval was erroneously associated with the presence of therapeutic benefits from the HDS. The survey also showed that FDA approval was significantly correlated with the presence of scientific evidence in favor of their claimed health benefits and safety (Cramer’s V=0.383, p<0.05).
Knowledge and understanding of the label “No Approved Therapeutic Claims” was also poor. The survey showed that only 24.0% of the respondents understood the label correctly. Those who did not understand it were also the ones who tended to believe that HDS can be used as alternative for prescription drugs (Chi square=10.7, p<0.05). Nevertheless, a number of participants from the interview and FGD were able to point out that products carrying this label should not be used as mainline drugs for the treatment of diseases, but rather as mere supplements only, and should not be expected to have any therapeutic benefits. Indeed, these results show that there is a need for further clarification and education of the public regarding what an FDA approval entails and what the label “No Approved Therapeutic Claims” really means.
Survey data showed a generally positive attitude by the respondents toward HDS. Most of the respondents expressed optimism regarding its perceived health benefits, whether for mere prevention of diseases (64.0%, p<0.05), slowing down disease progression (61.1%, p<0.05) or treatment of diseases (46.9%, p<0.05). Participants from the interview, especially those who experienced its supposed benefits from personal use, also showed a positive attitude toward it. Nevertheless, majority still believed that conventional drugs are more effective than HDS for the treatment of diseases (75.4%, p<0.05). FGD participants exhibited a rather mixed attitude toward HDS. Some believed in their effects while others doubted them.
Interview and FGD revealed an attitude favoring the safety of HDS due to the idea that they are “herbal” and therefore “natural”. Side effects from using HDS were perceived to be either absent or minimal. One FGD participant even narrated that a patient was cured by HDS because he took a lot of it. However, 53.2% of the survey respondents believed that there may still be harm in HDS when used excessively (p<0.05). Additionally, despite a generally positive attitude toward HDS, it was agreed by the participants that physicians must be consulted and informed regarding patients’ use of HDS.
Differing opinions emerged regarding the affordability of HDS. Survey data showed that 57.7% believed that HDS are not costly while 29.8% believed otherwise (p<0.05). Interview and FGD participants generally attested to the costliness of HDS. One reason why non-users chose not to use HDS was the financial drawback that comes along with it. Nonetheless, users who agreed that HDS are expensive continued to use them because they perceived that the positive attributes of HDS outweigh the negative attributes.
Despite the positive attitude toward HDS, survey respondents felt that the information being supplied by manufacturers regarding the safety of their products is still insufficient (62.9%, p<0.05). Those who believed that physicians must first be consulted regarding the use of HDS were found to be more likely to feel such insufficiency of information (Spearman’s rank=0.290, p<0.05). These results may indicate that there is indeed a desire by consumers to receive more information regarding HDS and there remains a degree of uncertainty with regard to their safety and health benefits as claimed. Furthermore, interview participants generally opted not to give recommendations to other people about the use of HDS. Users and non-users alike were hesitant in doing so. Users believed that they needed to have more experience in using them and to check for possible side effects before they start recommending them.
Survey showed that only 22.3% of respondents were HDS users while 89.7% were taking conventional drugs. Among the latter, 23.6% were also using HDS. Among HDS users, 94.9% were also taking conventional drugs. It is noteworthy that the population selected in this study represents those who believe in conventional medical therapy and are therefore consulting a physician. As such, it could be expected that a preference for the use of conventional drugs would be observed from the respondents. Indeed, only a minority reported to be HDS users. However, in a previous study by Cruz and Tanchoco in selected barangays in Metro Manila on the use of dietary supplements, only a minority (22.9%) also reported use of such products.9 Despite the fact that the said study was conducted in a community setting and the current study was done in a hospital setting, the results seemed to be consistent with each other.
Most interview participants reported intake of HDS at a different time in the day from their prescribed medications. Both users and non-users expressed the idea of possible drug interactions between HDS and their prescribed medications. Additionally, despite their use of HDS, users gave more priority to the intake of physician-prescribed drugs. Such behavior indicates that they do understand at least the basic difference between HDS and conventional drugs and that the former cannot serve as alternative for the latter. Among FGD participants, experience emerged as an important factor for intake. Positive outcomes from conventional treatment procedures favor one toward non- use of HDS or discontinuation of its intake.
Despite the belief of the majority that there is a need to inform physicians regarding one’s use of HDS, only 2 out of the 5 HDS users who were interviewed reported that they disclosed their use of HDS to their physicians. Reasons given for non-disclosure included the fear of being reprimanded and the perception that the use of HDS is “no big deal”. In the studies by Gardiner et al. and Mehta et al., only 24% and 33% of respondents, respectively, reported disclosing HDS use to health professionals.10,11 These show that disclosure to physicians is indeed not a very common practice among users.
Family emerged as an important motivation for HDS use. Consistent with the Filipino value of giving importance to one’s family and its welfare,12 certain users reported to use HDS as means of exhausting all possible ways to treat their ailments and make themselves healthy for the sake of their family. There were also those who were simply convinced by family members to use HDS. In addition to family, hiya and pakikisama were revealed to be motivating factors for the use of HDS as well.
For non-users, cost and physician’s approval emerged as important factors for their non-use of HDS. Majority expressed their willingness to use HDS if they would be provided for free. However, such willingness was observed to arise from the pervasive belief among the participants that HDS are “natural” and therefore harmless. Nevertheless, certain participants also expressed that they would finally use HDS after seeking their physician’s approval. It is noteworthy, however, that FGDs revealed the varying opinions of physicians regarding HDS use. This has brought some confusion among the patients and indeed points to a need for a unified stand and guidelines from the medical community concerning the matter.
Conceptual Framework and Conclusions
The conceptual framework generated from this study is shown in Figure 1. The knowledge and attitudes of an individual regarding HDS seem to affect largely his/her practices on HDS. Poor understanding of their difference from conventional drugs, their regulation by FDA and the meaning of the label “No Approved Therapeutic Claims” predisposes one to use HDS. On the other hand, good knowledge of their difference from conventional drugs and the meaning of “No Approved Therapeutic Claims” results in either non-use of HDS or use of HDS but as mere supplements to conventional drugs. Knowledge of possible drug interactions between HDS and prescribed drugs inclines one to take HDS at a different time in the day from his/her prescribed medications.
Figure 1. Conceptual framework on the knowledge, attitudes and practices of the study participants on the use of herbal dietary supplements (HDS)
Positive attitudes toward the claimed health benefits, safety, and affordability of HDS also predispose one to use HDS. On the other hand, costliness and physician’s lack of approval seemed to be factors that deter one from using HDS. A perceived insufficiency of information regarding HDS prompts one to feel the need to consult his/her physicians regarding HDS use, as well as not to recommend such products to others carelessly. Nevertheless, the fear of being reprimanded and an attitude toward HDS use as “no big deal” tend to sway an individual from disclosing his/her use of HDS to his/her physician.
In conclusion, proper knowledge on the nature and regulation of HDS, as well as an awareness of the current lack of information regarding their claimed health benefits and safety, results in judicious use or non-use of HDS. On the other hand, poor knowledge and positive attitudes toward their claimed health benefits, safety and affordability favor their use. Indeed, promoting accurate knowledge and proper attitudes toward HDS may thus serves as an effective way to modify the behavior of users or non-users with regard to HDS.
- Sia IC. Food supplements: friend or foe. PHILSPEN 5th Annual Convention; 2009 Nov 13; Manila, Philippines.
- Esplanada JE. Public warned vs food supplements [Online]. The Philippine Daily Inquirer. 2010 Jun 3 [cited 2011 May]. Available from http://newsinfo.inquirer.net/inquirerheadlines/nation/view/20100603-2735....
- Dietary Supplement Health and Education Act of 1994, Pub. L. No. 103- 417, 108 Stat. 4332. October 25, 1994.
- New York State Task Force on Life and the Law, Dietary supplements: balancing consumer choice and safety [Online]. 2005 [cited 2011 May]. Available from http://www.health.state.ny.us/regulations/task_force/docs/dietary_supple....
- Ulbricht K. Natural Standard Herbal Pharmacotherapy. St. Louis, MO: Mosby/Elsevier; 2010. pp. 4-5.
- Administrative Order 2010-0008, Office of the Secretary, Department of Health. March 18, 2010.
- Reyes MA. Overpriced carabao [Online]. The Philippine Star. 2010 Jun 6 [cited 2011 May]. Available from http://www.philstar.com/Article.aspx?articleId=581654& publicationSubCategoryId=66.
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- Cruz AJ, Tanchoco CC. Survey on awareness, perception, and extent of usage of nutraceuticals and dietary supplements in Metro Manila. J Med Food. 2000; 3(4):181-8.
- Gardiner P, Kemper K, Legedza A, Phillips R. Factors associated with herb and dietary supplement use by young adults in the United States. BMC Complement Altern Med [Online]. 2007 [cited 2011 May]; 7(39):[about 7pp.]. Available from http://www.biomedcentral.com/1472-6882/7/39.
- Mehta DH, Gardiner PM, Phillips RS, McCarthy EP. Herbal and dietary supplement disclosure to health care providers by individuals with chronic conditions. J Altern Complement Med. 2008; 14(10):1263-9.
- Anderson JN. Health and illness in Pilipino immigrants. West J Med. 1983; 139(6):811-9.