Homeopathy

INTRODUCTION — Homeopathy is a system of complementary and integrative medicine based upon the principle of "similars": the most appropriate treatment for an illness is a substance that causes the same symptoms when given to a healthy person. Homeopathic preparations are created through a process known as "potentization," in which the starting material is serially diluted and "succussed" (shaken). Homeopathic medicines include substances (ie, minerals, plants, or animal-derived materials) that are crushed, mixed with a water-alcohol solution, and then potentized multiple times, typically beyond the point which any of the original material theoretically remains.

Homeopathy and homeopathic medicines are distinct from herbal and dietary supplements; these are discussed separately.

●(See "Overview of herbal medicine and dietary supplements".)

●(See "Complementary and alternative treatments for anxiety symptoms and disorders: Herbs and medications".)

●(See "Chinese herbal medicine for the treatment of allergic diseases".)

●(See "Hepatotoxicity due to herbal medications and dietary supplements".)

●(See "Complementary and integrative health in pediatrics".)

EPIDEMIOLOGY OF HOMEOPATHIC PRACTICE — Homeopathy is less commonly used in the United States than in countries in Europe and Asia [1-3]. In a 2012 National Health Interview Survey (NHIS) evaluating the use of complementary and integrative medicine in the United States, 2.2 percent of adults and 1.8 percent of children ages 4 to 17 years had used homeopathic medicines within the past year [4,5]. Most individuals using these medicines had self-treated with over-the-counter products and did not see a homeopathic provider for guidance [6]. However, among those taking homeopathic medicines, those who saw a homeopath were more likely to find the treatment helpful than those who did not. The most common categories of problems treated with homeopathic medicines included respiratory and otolaryngological (18.5 percent), musculoskeletal (12.3 percent), fatigue, sleep problems, stress or chronic pain (7.7 percent), gastrointestinal (5.0 percent), neurologic (3.4 percent), and mental health (2.1 percent).

FOUNDATIONS OF HOMEOPATHY

Principle of similars — Homeopathy was created in the late 1700s by the German physician Samuel Hahnemann after noting that ingestion of the bark of Cinchona officinalis (later found to contain quinine), which was used for the treatment of malaria, caused symptoms similar to malaria [7]. Based upon this observation, Hahnemann concluded "similia similibus curantur" or "likes are cured by likes."

Although the principle of similars is not unique to homeopathy (precursors are found in the Hippocratic corpus and writings of Paracelsus), Hahnemann was the first to integrate this principle into an entire system of therapeutics.

Homeopathic pathogenetic trials — Based upon Hahnemann's observations, experiments (or "provings") were performed with human volunteers, comparing the effects of substances with placebos. In fact, early homeopaths conducted some of the first placebo-controlled trials [8].

Creation of homeopathic medicines — Homeopathic medicines are manufactured according to a process known as potentization (also referred to as "attenuation" or "dynamization"). Many of the conventional medicines of Hahnemann's time (eg, arsenic, mercury, belladonna) were toxic, and initial provings were done with undiluted substances. He experimented with attenuating the dose of homeopathic preparations through serial dilutions and succussions; this process not only reduced the adverse effects but, according to his observations, paradoxically seemed to render the preparations more potent.

Most modern homeopathic preparations similarly begin with a mineral, plant, or animal material that is pulverized and mixed with a water-alcohol solution or triturated in lactose [9].

The dose of a homeopathic medicine is indicated by a combined number-letter designation, with the number representing the total number of potentization steps and the letter representing the degree of dilution at each step (eg, the roman numeral "X" or a "D" for 1:10 dilutions, and the roman numeral "C" for 1:100 dilutions) [7]. As examples:

●A homeopathic preparation with a 6X potency has undergone 6 serial potentizations with a 1:10 dilution at each step; the final concentration is 10^-6 from the starting material.

●A homeopathic preparation with a 30C potency has undergone 30 serial potentizations with a 1:100 dilution at each step; the final concentration is 10^-60 from the starting material.

Homeopathic medicines are commonly diluted from 10^-6- to 10^-10,000-fold; medicines diluted beyond 10^-23 are sometimes called ultra-high dilutions, ultramolecular dilutions, or ultra-low doses. Once potentized, most medicines are applied to small lactose or sucrose pellets, which are taken sublingually. Homeopathic medicines can also be manufactured as injectable, liquid (for oral use), or topical preparations.

Homeopathic medicines are manufactured by dedicated pharmaceutical companies following specific criteria outlined in the Homeopathic Pharmacopoeia of the United States (HPUS) or similar documents [10-12].

Homeopathic reference materials — Homeopathic practitioners consult reference material to determine the most appropriate medicine to treat a specific symptom or constellation of symptoms. Books, collectively known as "materia medica," contain information on available medicines including descriptions of symptoms that they both elicit and treat, as well as toxicological information on the foundation substances. A repertory is a reference book in which symptoms, listed alphabetically and grouped by organ systems and anatomic location, are followed by a list of homeopathic medicines that can treat the symptom. In addition, medicines are typically ranked according to the degree that they produce the symptom.

Historically, the process of matching symptoms to medicines was tedious, performed by cross-referencing between different books; computer software has greatly aided this process.

Homeopathic approach to selecting a medicine — The homeopathic practitioner elicits a detailed description of a patient's symptoms, then consults a repertory to identify the medicine that most closely matches the totality of symptoms. The process is repeated for all of the patient’s symptoms (or in some cases, the most characteristic symptoms), creating a list that can be further narrowed by consulting a materia medica.

This process leads to individualized treatment of the unique manifestations of an illness in a particular patient. For this reason, two patients with the same disease process, but with slightly different symptoms, may be prescribed different homeopathic medicines. As an example, a patient with a viral upper respiratory tract infection who presents with a thin, clear nasal discharge with irritation and stinging of the eyes may be treated with a preparation made from onion (Allium cepa), while another patient with the same infection who has thick, yellow nasal discharge with loss of thirst may be treated with Pulsatilla, a preparation made from the pasque flower [13].

Styles of contemporary homeopathy — There are several different styles of homeopathy that are commonly practiced today [7], including classical, clinical, and complex homeopathy.

●Classical homeopathy – Classical homeopathy involves the method described above, in which the totality of the patient’s symptoms is taken into account to find the most appropriate homeopathic medicine. Generally, only one medicine is prescribed at a time. There are a variety of different schools of classical homeopathy that follow variations on this approach.

●Clinical homeopathy – Clinical homeopathy generally focuses on a narrower subset of symptoms, using a more pathophysiologic approach and treating with lower potency (less dilute, usually no higher than 30C) medicines. In clinical homeopathy, multiple homeopathic medicines may be prescribed at once, each medicine for a specific indication.

●Complex homeopathy – Complex homeopathy uses multiple homeopathic medicines combined into a single compound to target a symptom complex (eg, allergic rhinitis) in an attempt to cover the natural variation in symptoms for a large majority of patients. Such preparations are typically low potency (less dilute) and are widely available over the counter.

LIMITED EVIDENCE SUPPORTING THE USE OF HOMEOPATHY

Clinical outcomes — Data supporting the use of homeopathic medicines for treatment of clinical conditions are limited.

Meta-analyses of randomized trials of homeopathic treatment are limited by the quality of available trials [14]. As examples, in a 2017 meta-analysis including 54 trials of non-individualized homeopathic treatments for a wide variety of conditions, only three included trials were judged to be high-quality with low risk of bias [15]. Similarly, in a 2014 meta-analysis including 32 trials of individualized homeopathic treatments for various conditions, only three included studies were considered reliable [16].

High-quality data supporting the superiority of homeopathic treatment over placebo are lacking. Although several meta-analyses reported an overall benefit of homeopathic medicines in general (rather than for a specific medical condition) compared with placebo, most of the included trials were deemed low quality [17-19]. No significant effect was found when only the highest-quality trials were analyzed [19].

Conversely, high-quality data that homeopathic treatment is equivalent to placebo are also lacking; meta-analyses making this claim [20,21] have significant methodologic problems that limit their conclusions [22-25].

Limited evidence suggests that homeopathic medicines may possibly be useful for the symptomatic management of certain conditions, including allergic rhinitis [26], viral upper respiratory tract infection in children [27], ecchymosis following rhinoplasty and facial procedures [28,29], and fibromyalgia [30].

However, systematic reviews and meta-analyses of randomized trials evaluating homeopathy for other specific conditions have failed to show evidence of benefit (eg, attention deficit/hyperactivity disorder [31,32]) or concluded that there was insufficient evidence to determine whether homeopathy was effective (eg, asthma [33], dementia [34], urologic disorders [35], and irritable bowel syndrome [36]). A meta-analysis evaluating the efficacy of homeopathy for the management of acute upper respiratory tract infections in children found no benefit [32], but the study had methodologic limitations and also did not include a large, high-quality trial that did demonstrate efficacy [27].

Controversies — In addition to the limited high-quality data supporting the overall efficacy of homeopathy, the assertion that the medicines are rendered more potent with increased numbers of serial dilutions and succussions is another reason that homeopathy remains contentious; homeopathy seems to defy logic and the biomedical paradigm [22].

Nonetheless, there exists materials science, botanical, cell and molecular, and zoological experiments that support the foundational principles of homeopathy [9,22,37-48]. As an example, materials science research has demonstrated the presence of source nanoparticles in homeopathic preparations [41,42,45]; these may modulate the stress response network and have possible hormetic effects [9,46-48].

Safety — Treatment with homeopathic medicines, particularly oral and topical formulations, is generally safe. As an example, in a meta-analysis including 41 trials and over 6000 patients, homeopathic treatment had no more side effects than placebo (odds ratio [OR] 1.03, 95% CI 0.89-1.20) [49]. Furthermore, in a German study evaluating post-marketing adverse drug effects of injectable homeopathic preparations, there were less than four reactions per one million ampules sold, with at least a quarter of these being a local injection site reactions [50].

However, since 2009, the US Food and Drug Administration (FDA) has recalled several over-the-counter homeopathic products due to mislabeling. In one case, the product was mislabeled as homeopathic but actually contained sizeable amounts of zinc, which led to anosmia in some individuals [51]. In another case, a product was marketed for asthma symptoms, a non-over-the-counter indication that is not permitted [52]. In 2017, the FDA recalled homeopathic teething tablets, some of which contained atropine and scopolamine in excess of the labeled quantities [53]. However, of the over 400 possible patient incident reports filed with the FDA, the majority were requests for information and not reports of harm [54].

REGULATION OF HOMEOPATHY

Regulation of homeopathic medicines — The regulation of homeopathy and homeopathic medicines varies globally [55]. In the United States, the Homeopathic Pharmacopoeia Convention of the United States publishes the Homeopathic Pharmacopeia of the United States (HPUS), the guide for manufacturing homeopathic medicines [56,57]. Prior to 2017, the US Food and Drug Administration (FDA) recognized the HPUS, with minimal regulatory interference in the marketing of homeopathic medicines. In 2017, the FDA issued draft guidance recommending more rigorous regulation of homeopathic medicines [58]; that draft guidance was revised in 2019 [59]. The FDA has recommended a "risk-based" enforcement approach for the marketing of certain homeopathic preparations, such as those that purport to treat more serious health conditions (eg, asthma), those that are intended for use in vulnerable populations (eg, infants and children, older adults, and pregnant individuals), and those that are intended for administration other than an oral or topical route.

There are no homeopathic preparations or products marketed in the United States that are FDA approved.

Certification of homeopathic practitioners — In North America, there are several homeopathic certification boards, many of which provide publicly available lists of certified practitioners. As examples, the American Board of Homeotherapeutics grants the Diplomate of Homeotherapeutics (DHt) certificate to Medical Doctors (MDs) or Doctors of Osteopathy (DOs) [60], and the Homeopathic Academy of Naturopathic Physicians grants the Diplomate of the Homeopathic Academy of Naturopathic Physicians (DHANP) certificate to naturopaths [61]. The Council for Homeopathic Certification (CHC) confers a Certified Classical Homeopath (CCH) designation to lay practitioners [62]. Practitioners certified by the CHC can become members of the North American Society of Homeopaths (NASH), using the designation "RSHom (NA)" [63].

SUMMARY

●Principles of homeopathy – Homeopathy is a system of complementary and integrative medicine based upon the principle of "similars": the most appropriate treatment is a substance that, when given to someone without a given condition or illness, produces symptoms similar to those experienced by an individual with the condition. Homeopathic preparations are created through a process known as "potentization," in which the starting material is serially diluted and "succussed" (shaken). Homeopathic preparations are potentized multiple times, typically beyond the point which any of the original material theoretically remains. (See 'Introduction' above.)

●Doses of homeopathic preparations – The dose of a homeopathic medicine is indicated by a combined number-letter designation, with the number representing the total number of potentization steps and the letter representing the degree of dilution at each step. Homeopathic medicines are commonly diluted from 10^-6- to 10^-10,000-fold; medicines diluted beyond 10^-23 are sometimes called ultra-high dilutions, ultramolecular dilutions, or ultra-low doses. (See 'Creation of homeopathic medicines' above.)

●Limited data supporting clinical efficacy – High-quality data supporting the efficacy of homeopathic medicines for the treatment of clinical conditions are limited. While there are some high-quality trials that support the efficacy of homeopathy in the treatment of certain conditions, many trials are limited by methodologic problems. (See 'Clinical outcomes' above.)

●Safety – Treatment with homeopathic medicines, particularly oral and topical formulations, is generally safe. (See 'Safety' above.)

●Regulation – The US Food and Drug Administration (FDA) has recommended a "risk-based" enforcement approach for the marketing of certain homeopathic preparations, such as those that purport to treat more serious health conditions (eg, asthma), those that are intended for use in vulnerable populations (eg, infants and children, older adults, and pregnant individuals), and those that are intended for administration other than an oral or topical route. There are no homeopathic preparations or products marketed in the United States that are FDA approved. (See 'Regulation of homeopathic medicines' above.)

ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Kimball Atwood, MD, who contributed to an earlier version of this topic review.