Use of Herbal Therapies to Relieve Pain: A Review of Efficacy and Adverse Effects

James H. Wirth, BA; J. Craig Hudgins, BA; Judith A. Paice, PhD, RN

Pain Manag Nurs. 2005;6(4):145-167. 

Abstract and Background

To find holistic treatment with effective pain relief and few side effects, Americans spend billions of dollars annually on complementary and alternative medicine, including herbal therapies. Despite extensive use, the lack of regulatory scrutiny of these herbal supplements contributes to the paucity of reliable clinical data assessing their efficacy and safety. This review summarizes the existing studies investigating the efficacy of herbal therapies as a treatment for pain. Possible side effects, potential drug–herb interactions, and information about common herbal therapies are also summarized. MEDLINE, AMED, and the Cochrane Library databases were searched for the period from January 1966 to June 2005. Uses, dosages, routes of administration, and side effects were summarized. Strength of empirical evidence also was evaluated. This review found few well-controlled clinical studies. Furthermore, these studies documented limited efficacy of herbal therapies to treat pain. The information presented here may be used to further educate nurses and patients on the use of herbal therapies as well as direct future research efforts.

Patients experiencing pain may try numerous therapies, including conventional and alternative approaches, for relief. Pain relief is the most frequently cited reason that people seek complementary and alternative medicine (CAM) (Astin, 1998). CAM encompasses therapeutic treatments such as relaxation, meditation, biofeedback, hypnosis, imagery, chiropractic, acupuncture, massage, aromatherapy, and herbal therapies. A 2002 study conducted by the National Center for Complementary and Alternative Medicine surveyed 31,044 adults and found that 36% of respondents used some form of CAM therapy during the last 12 months (Barnes, Powell-Griner, McFann, & Nahin, 2004). These therapies might be chosen because other conventional therapies were previously ineffective or produced side effects that were intolerable. Therefore, clinicians must be aware of CAM therapies used to treat pain to answer questions from patients effectively and to avoid possible interactions with medical (drug) therapies prescribed for patients.

Reasons for Using Complementary and Alternative Medicines

CAM users choose alternative therapies so their health care is more congruent with their personal values, beliefs, and overall philosophic orientation toward health and life (Astin, 1998). This philosophical orientation may result from personal values, past health care experiences (i.e., disillusionment with conventional therapies because of their lack of efficacy or side effects), or desire to have control over health care matters (Astin, 1998; Barnes et al., 2004).

Many herbal therapy users have a chronic disease. A study by Boon and colleagues (2000) reported that some patients with breast cancer chose CAM to boost their immune system, increase quality of life, prevent recurrence of cancer, provide a feeling of control over life, aid conventional medical treatment, or treat breast cancer. The most frequently cited health problems that lead to CAM use are anxiety, back problems, chronic pain, and urinary tract disorders (Astin, 1998). According to studies by Barnes et al. (2004) and Kimby, Launso, Henningsen, and Langgaard (2003), women and older adults are most likely to seek CAM therapy, and CAM users generally perceive the treatments have fewer side effects than do conventional medicines (Eisenberg, et al., 2001).

Unfortunately, those who use CAM face potential adverse side effects, including drug–herb interactions. Thus, clinicians in the pain field should be familiar with the uses and potential risks associated with CAM. More than half of patients first seek information related to CAM therapies from their primary physician (Eisenberg et al., 2001). Hyodo and colleagues (2003) found that 93% of Japanese clinical oncologists surveyed in 2002 had been asked about CAM options. In this study, 80.2% responded they were unable to advise their patients appropriately about the use of CAM products. Similarly, Eisenberg, Kessler, Foster, Norlock, Calkins, and Delbanco (1993) reported that physicians do not discuss the use of unconventional therapies because they lack adequate knowledge of these techniques. Other barriers to discussion regarding CAM exist, including patients perceiving that clinicians lack interest (Verhoef, Hilsden, & O'Beirne, 1999), are closed-minded, lack knowledge (Eliason, Huebner, & Marchand, 1999), and would not understand or would not approve of the alternative therapy (Eisenberg et al., 2001).

Surprisingly, negative attitudes toward or experiences with conventional medicine do not predict CAM use (Astin, 1998), despite one stereotype that CAM users are disgruntled patients. CAM users are frequently no more dissatisfied or distrustful of conventional practitioners and hospitals than nonusers (Astin, 1998). Most complementary therapies are used in conjunction with conventional medicine (Eisenberg et al., 2001). In a national survey, 79% of respondents believed that the combination of conventional and alternative therapies is more effective than either approach alone (Eisenberg et al., 2001), and presumably this desire for a more holistic approach to health care is what accounts for $21.2 billion in U.S. consumer spending in 1997 on CAM professional services (Rees, 2001), including massage, acupuncture, chiropractic treatment, and herbal therapies.

Herbal Therapy Use for Pain

Herbal therapies are more likely to be used by those with a better education, poorer health status, and a holistic orientation to health; those wanting relief from symptoms or seeking improvement in their general condition; and those who had a transformational experience that changed their world view (Astin, 1998; Kimby et al., 2003; Oldendick et al., 2000). The most commonly used natural products are echinacea, ginseng, ginkgo biloba, and garlic supplements (Barnes, et al., 2004). In the United States, approximately $4 billion per year is spent on herbal products, with an annual growth of more than 30% (Rees, 2001). During the 1990s, there was an estimated 380% increase in the sale of herbal substances. In 2002, a survey found 19% of adults had used natural products such as herbal medicine, functional foods (garlic), or animal-based supplements (Barnes, et al., 2004). Approximately $76 million was spent in 2002 for just three of these supplements alone: androstenedione, kava, and yohimbe (Dangerous Supplements: Still at Large, 2004).

The use of herbal therapies comes with potential risks that are worth noting to consumers of herbs for medicinal purposes. Active ingredients in herbal therapies or drugs may produce herb/herb or herb/drugs interactions that have undesirable side effects (Ernst, 1998; Fugh-Berman & Ernst, 2001). For example, when combined with levodopa, kava can cause an increase in the number and duration of "off" periods; St. John's wort taken with sertraline (Zoloft) may produce nausea, vomiting, or anxiety (Fugh-Berman & Ernst, 2001). Herbal therapies and drugs are often made of more than one active element. This further complicates what pharmacologic ingredient is causing the interaction or undesirable side effect (Izzo & Ernst, 2001; Fugh-Berman & Ernst, 2001).

A lack of standardization of herbal remedies also makes it challenging to understand what causes adverse interactions. Contamination, misidentification of an herbal plant, or an incorrectly substituted plant all raise issues of quality (Drew & Myers, 1997; Ernst, 1998) and can result potentially in an unwanted side effect. Of 400 users of complementary medicine surveyed, Abbot, White, and Ernst (1996) found 8% of those who tried herbal remedies had an adverse reaction.

Incorrect preparations, incorrect dosages, lack of standardization, substitution, or improper processing of plants can result in unwanted combinations of ingredients in herbal therapies (Drew & Myers, 1997; Ernst, 1998). The pharmacologically active component may not necessarily be known, making it difficult to understand how the therapies work (Ernst, 2000). Unwanted ingredients may lead to contamination, for example, when bovine spongiform encephalopathy from bovine organs was found in dietary supplements (Department of Agriculture, 2000; Scott et al., 1999). Cassileth and Deng (2004) contend that herbs are diluted natural drugs that contain scores of different chemicals that may not have been documented. A CAM user may not anticipate the potential interactions with other medications or herbal preparations.

A lack of strict government regulation diminishes efforts at prevention of potentially harmful results of herbal remedies. In 1994, Congress passed the Dietary Supplement Health and Education Act (DSHEA) to set regulation standards of herbal therapies for medical benefit. DSHEA relieved pressure from the U.S. Food and Drug Administration (FDA) on herb manufacturers to prove health benefits of herbal therapies, thereby permitting them to make it to the marketplace without demonstrating any benefits (Larsen & Berry, 2003). This creates a difficulty, because 59% of respondents to an Internet survey believe herbal products must be approved by a government agency similar to the FDA (Widespread Ignorance of Regulation and Labeling of Vitamins, Minerals and Food Supplements, According to a National Harris Interactive Survey, 2002).

DSHEA also allows herbal manufacturers to make three types of claims without FDA approval: (1) nutrient content claims, (2) health claims, and (3) nutrient support or structure-function claims (Kurtzweil, 1998; Overview of Dietary Supplements, 2001). Limited federal authority has led to animal products being included in dietary supplements, increasing the possibility of contamination. Consumers need to be wary of false claims, insufficient labels, and the potential for animal products to be included in the herbal therapy.

Those individuals considering herbal therapy use for pain control also may struggle to find credible sources of information. A recent U.S. investigation suggests that information provided by health food stores can be dangerously misleading, because potentially uneducated health food store employees may freely give advice about treatment for life-threatening illnesses (Phillips, Nichols, & King, 1995). Likewise, prominent herbal therapy product web sites often convey incorrect information (Morris & Avorn, 2003). A review of Internet web sites found 273 (81%) of 338 sites made one or more health claims that may or may not be proven.

Labels on herbal products also are not a reliable source of information, often missing important details such as product's safety, effectiveness, or possible side effects (Zuk, 2000). This lack of information runs contrary to what the general population believes is included on herbal product labels. In a study of knowledge of regulations and labeling of food supplements, 68% of survey respondents believed the government requires label warnings on potential side effects or dangers (Widespread Ignorance of Regulation and Labeling of Vitamins, Minerals and Food Supplements, According to a National Harris Interactive Survey, 2004). Ultimately, relaxed regulation places the onus on clinicians to educate and protect patients. As people with pain frequently turn to CAM for relief, pain management nurses must be aware of the risks and benefits of CAM for pain control.

Methods

To identify articles on the use of herbal therapies to reduce pain, a literature search of MEDLINE (January 1966 to June 2005), AMED (Allied and Complementary Medicine, January 1985 to June 2005), and the Cochrane Library (November 2003 to June 2005) databases was conducted. Reference lists of articles identified from the initial search were also reviewed for additional articles. Research conducted with humans or animals was reviewed. Only English language publications were considered. Search criteria comprised the term pain with the common name, Latin name, and common synonyms for the herb in question (e.g., for Black cohosh, search criteria pain and baneberry, cimicifuga, and bugbane each were used). Most articles were identified using the herb's common or Latin name.

All English-language titles and abstracts, from January 1966 to the present, were evaluated for inclusion in this review. The first articles on herbal therapies to reduce pain were published in 1990. All pain syndromes were considered for this review. Publications written in English in which an herb was studied to determine its effect on reducing pain or investigated in a human or rodent trial were included. The review resulted in a range of articles addressing several types of pain syndromes treated with the use of herbal therapy.

Methodologic quality of the studies reviewed was evaluated using a scientific evidence scale published by the U.S. Department of Health and Human Services (Jacox et al., 1994). The type of evidence and the strength and consistency of the evidence were recorded for all of the studies included in this review. Types of evidence were (1) meta-analysis, (2) at least one well-designed experimental study, (3) well-designed quasi-experimental studies, (4) well-designed nonexperimental studies, and (5) case reports and clinical examples ( ). Strength and consistency of evidence were (1) consistent findings from multiples studies, (2) findings that are generally consistent, (3) findings are generally inconsistent, (4) little or no evidence ( ).

  Strength of Evidence (Jacox et al., 1994)

  Strength of Evidence (Jacox et al., 1994)

This review of commonly used herbal therapies used to treat pain includes information about possible known uses, dosages, and routes of administration. It also includes safety and adverse effect information. This information was collected primarily from the Natural Medicine Comprehensive Database (2003) and several other published sources (Nutrition in Cancer Care, 2004; Skidmore-Roth, 2004; The Complete German Commission E Monographs: Therapeutic Guide to Herbal Medicines,1998; Koenig, 2003). Several web sites were identified, and content from them was incorporated into the review. These are listed in .

  CAM-Related Informational Web Sites

Results

In our search of herbal therapies, 34 publications describing the use of 24 herbal therapies to treat pain were identified ( ). Ten of the 24 (42%) herbal therapies had research evidence available investigating the ability of the herbal therapy to manage pain. For the remaining 16 herbal therapies (58%), no known research on their use in pain management was identified at the time of this review. The herbal therapies that were proven effective were useful when specifically treating arthritis (Brzeski, Madhok & Capell, 1991; Deal et al., 1991), polyneuropathy (Low, Opfer-Gehrking, Dyck, Litchy, & O'Brien, 1995), postmastectomy pain syndrome (Dini, Bertelli, Gozza, & Forno, 1993; Watson & Evans, 1992), neuropathy (Scheffler, Sheitel, & Lipton, 1991), or low-back pain (Chrubasik, Eisenberg, Balan, Weinberger, Luzzati, & Conradt, 2000; Frerick, Keitel, Kuhn, Schmidt, Bredehorst, & Kuhlmann, 2003). The quality of the identified studies ranged from a meta-analysis of multiple studies producing consistent findings (Type I, A) to case reports that had generally consistent findings (Type V, B; ). Overall, most of the research had at least one well-designed experimental study that produced evidence that was generally consistent. This review found only four double-blind, randomized, controlled trial studies (Deal et al., 1991; Low et al., 1995; Jeffrey & Belcher, 2002; Sindrup, Madsen, Bach, Gram, & Jensen, 2001).

  Herbal Therapies for the Relief of Pain

  Strength of Evidence (Jacox et al., 1994)

Studies for only 10 of 24 herbs used to manage pain successfully were reviewed for efficacy. Of these 10 herbals, several studies used a placebo-controlled study methodology to investigate the herbal therapy's effectiveness (Altman & Marcussen, 2001; Brzeski, Madhok, & Capell, 1991; Chrubasik et al., 2000; Deal et al., 1991; Dini et al., 1993; Ellison et al., 1997; Frerick et al., 2003; Low et al., 1995; Scheffler, Sheitel, & Lipton, 1991; Watson & Evans, 1992). In addition, several studies found that herbal therapies were no more effective at managing pain compared with a placebo or general pain medication (Bliddal et al., 2000; Ernst & Pittler, 1998; Kaziro, 1984; Paice, Ferrans, Lashley, Shott, Vizgirda, & Pitrak, 2000; Sindrup et al., 2001).

Many of the herbal therapies had significant adverse side effects that should be considered when using these treatments. For example, Arnica is considered poisonous if injected and may also cause liver damage (Skidmore-Roth, 2004). In 2004, Ephedra was banned because of its increased risk for heart palpitations, tremors, and insomnia. This was the first time U.S. officials blocked the sale of an over-the-counter herbal supplement (Government Announces Ban on Ephedra, 2004). Overall, common side effects caused by the investigated herbal therapies included nausea, vomiting, burning sensations, gastrointestinal irritation, intestinal blockage, and insomnia. Adverse interactions with numerous drugs and the possibility of worsening medical conditions were common to many of the herbal therapies we investigated. For example, herbal therapies may worsen diabetes for some patients or estrogen-sensitive hormone disorders in some women (Natural Medicine Comprehensive Database, 2003; Nutrition in Cancer Care, 2004; Skidmore-Roth, 2004; The Complete German Commission E Monographs: Therapeutic Guide to Herbal Medicines, 1998).

A review conducted by Fugh-Berman and Ernst (2001) of suspected interactions of herbal therapies and other treatments found warfarin was the drug most likely to be involved in adverse interaction with an herbal therapy, and St. John's wort was the herbal therapy most likely to cause an adverse interaction. Although many herbs have potential side effects, several herbal therapies reviewed have a status of "Generally Recognized as Safe" for food use in the United States (chamomile, cinnamon, cloves, ginger, mustard) (Natural Medicine Comprehensive Database, 2003).

Discussion

The use of herbal therapies is an increasingly popular method to treat pain, either alone or as a complement to traditional medical approaches. Unfortunately, research demonstrating the efficacy of herbal therapies to treat pain is limited. The strongest evidence identified in this analysis was Type I, A, found in only one study. For the majority of the herbal therapies reviewed, there was no empirical evidence for the analgesic efficacy of these compounds. Questions still remain about their underlying mechanisms to provide analgesia (Ernst, 2000). As the use of herbal therapies grows, empirical research demonstrating their benefits in pain control lags. The establishment of the National Center for Complementary and Alternative Medicine supports research of herbal therapies and other CAM.

In regard to the safety of herbal therapies, several possible drug and herbal interactions were identified. Understanding these interactions is complicated by the fact that the precise composition of many herbal therapies is not fully known. Impurities and lack of quality testing may result in elements in herb mixtures that are not intended to be included. Furthermore, patients may be lured into a false sense of security believing that because herbal therapies are "natural" and are not regulated by the FDA, they are inherently safe. These misconceptions may lead herbal therapy users to believe the therapies are safer than they really are.

It is important for nurses to openly communicate with patients who use CAM therapies. With use of herbal therapy on the rise, nurses are encouraged when taking drug histories to routinely ask for information about a patient's use of CAM therapies (Drew & Myers, 1997). It is important to be nonjudgmental and to keep in mind that patients may not consider "natural" substances in the same way as pharmaceuticals. When addressing adverse drug reactions, question possible CAM use, do not discount long-term use of CAM preparations as causing side effects because there may be batch-to-batch differences, and contact Drug and Poison Information Centers for information on CAM relating to a suspected adverse drug reaction (Drew & Myers, 1997). Education on what is understood about herbal therapies may also greatly benefit the patient. Education about alternative means to treat pain, such as medication or another CAM therapy, may also be suggested. To learn more about CAM, a list of educational web sites is included ( ).

  CAM-Related Informational Web Sites

This study is limited by several methodologic constraints. Publications were identified using only three search engines; more publications may have been identified through more diverse search means. In addition, only publications written in English were reviewed. There may be a larger body of research in non-English speaking countries, where use of herbal therapies is more prevalent. Review and translation of these articles were beyond our resources.

Conclusion

The use of CAM, especially herbal therapies, to reduce pain has dramatically increased. Although use has increased, scientific evidence of the efficacy of herbal therapies to moderate pain is still limited. This review summarized the empirical evidence available for 24 herbal therapies and also detailed uses, dosages, routes of administration, and side effects related to these herbal therapies. This information will help pain management nurses educate themselves about herbal therapies to be better equipped to advise and treat patients who use herbal therapies.Government announces ban on ephedra 2003

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