Homeopathy is hugely popular in many countries, with the volume of the industry being hundreds of million euros in Germany and close to three billion dollars in the USA [1]. However, despite its popularity, the conversation about the efficacy of homeopathy is becoming increasingly controversial and many medical professionals and scientists even call homeopathy a sham [2].

In this article, we present the main principles of homeopathy, take a look at scientific literature that covers the effectiveness of homeopathy, and discuss the impact of continued support of homeopathic treatments on patients and society.

The homeopathic method was invented by the German physician Samuel Hahnemann by the end of the 18th century and it is based on two fundamental principles – ‘like cures like’ and the heavy dilution of pharmacologically active substances [3, 4]. The idea of the first principle is that substances that generate certain symptoms in healthy people can be used to cure the same symptoms in sick people. A popular example is that onions cause a runny nose and hence they are a suitable cure for the common cold. This principle has its roots in middle age medicine and all findings of modern pharmacology indicate that it is not that simple. The second principle states that the more an active substance is diluted, the more powerful of a remedy it becomes. The rationale behind this principle involves esoteric ideas like the transfer of ‘vital energy’ from the substance to the solvent via rigorous shaking, called ‘succession’ [5]. This principle is in direct conflict with basic chemical principles like the ‘law of mass-action’, which states that more effect can only be achieved with more material – e.g. more fire can only be caused by more wood. Dilutions of 1:10^60 are commonly found in homeopathic compounds [1], which equates to one molecule in about 100 trillion times the volume of all oceans on earth. Therefore, the probability of a homeopathic compound containing at least one molecule that is not solvent – e.g. water – are negligible.

The two principles that homeopathy is based on are inherently non-scientific and hence it is not surprising that the efficacy of homeopathy as a remedy for any medical condition has not yet been demonstrated in a way that would be required for conventional medicine like antibiotics or painkillers [6]. In fact, homeopathic compounds are often legally exempted from standard pharmacological tests such as clinical trials, because they lack pharmacologically active ingredients and their efficacy can hence not be demonstrated in a scientifically rigorous manner [7]. Even studies by homeopathy manufacturers failed to present compelling evidence so far [1] and all work indicating effectiveness of homeopathic therapies has been later retracted or discredited due to poor scientific conduct [8]. 

The only effect of homeopathic compounds that can be shown in clinical trials is the placebo effect. For example, multiple studies have demonstrated that the popular homeopathic compound ‘Arnica’ relieves pain as effectively as preparations with no pharmacologically active substances [9]. It is true that in certain circumstances the placebo effect can work towards treating medical conditions. However, it is very unreliable as it varies greatly both between patients and individuals on a day-by-day basis and is therefore not suitable as a medical treatment strategy [10].

For individual patients, the use of homeopathy as an exclusive therapy is hence ineffective at best and potentially harmful if effective and approved therapies are avoided. Moreover, the prescription of homeopathy by medical professionals despite the lack of evidence for its efficacy can be regarded as unethical and in direct conflict to the Hippocratic Oath. Furthermore, the continued support of homeopathic therapies by health insurances – e.g. in Germany – may lead to the diversion of crucial resources away from scientifically tested and effective treatment strategies, and gives homeopathy the appearance of integrity [1].

Resolving these issues will require time and effort on the side of law-makers, scientists, and science communicators. One key step will be to introduce evidence-based testing of homeopathic compounds prior to their release (and retrospective testing of released compounds), as is standard for all pharmacological substances. Moreover, scientists and journalists should take active part in the public discourse about homeopathy by supplying empiric facts about the fundamentals and efficacy of the homeopathic method. Hopefully, this way we can achieve what all sides of this argument can agree on: safe and effective medicine.