The Principle of Similars in Medicine

The simile principle, which was already described when homeopathy was given its name, first appeared in Hahnemann's writings in 1796:

"... One (...) applies to the (especially chronic) disease to be cured that medicine which is able to excite another, as similar as possible, artificial disease, and the latter will be cured; Similia similibus. ..." (Hahnemann, 1796)

In a modern version based on a stimulus-response model, the formulation would be based on the original:

... In order to trigger a curative reaction, in the predominantly chronic diseases to be treated, select the drug that can elicit a physiological response that is as similar as possible to the description of the symptoms of the disorder or the disease - similia similibus.

Although the homeopathic therapeutic principle of action has been proven experimentally and empirically over the last 225 years through the use of remedies according to the simile concept (see below), it does not appear very plausible at first glance on the basis of current pharmacology, which is characterised by the natural sciences.

The dispute about the term and its definition as a similarity law or rule, principle or simply similarity theorem or concept, is and has been conducted intensively in phases without achieving a conclusive scientific evaluation (Jütte, 1997)

To clear up any misunderstandings once and for all, it should be emphasised that the term "principle" does not refer to a law of nature, but rather describes a stringent system, the smallest possible algorithm required to produce a specific effect. As a result of the resulting simplicity, such a systematic principle can often be transferred from one therapy system to another (also on an interdisciplinary basis).

For homeopathic therapy it therefore makes sense to speak of a drug prescription concept, while the overarching idea itself, if it is also found in other areas of medicine, can be described as a systematic principle.

Simile principle in medicine

A closer look reveals some indications that, at least indirectly, numerous confirmations of this active principle can be found in the practice of conventional medicine. Despite their wide range of applications, they exist more as an incidental marginal phenomenon. These include:

• Everyday observations, such as rubbing cold hands with snow in winter,
• The same applies to the current guideline recommendation to treat minor burns with heat rather than cold to relieve pain,
• the systematic therapeutic regulatory impulse of hydrotherapy (thermal stimuli in the same direction),
• Specific concepts for intestinal reorganisations,
• non-specific stimulation therapies, such as autologous blood treatments, e.g. in orthopaedics, and
• Direct current therapy (galvanisation), which causes inflammation-like reactions in the tissue,
• X-ray irradiation and skin irritation therapies for chronic pain,
• ischaemic pre-post conditioning as a therapy in cardiology,
• immunological procedures, such as BCG implementation for bladder carcinoma,
• Vaccinations and autovaccines, which are intended to induce immunisation through modulated pathogens, sometimes combined with immunostimulant additives,
• immunological procedures such as interferon fever therapy, which induces and strengthens the body's own immune reactions,
• Desensitisation to allergens
• Empathy-based methods of humanistic psychotherapy, such as containing[1] , also work on the basis of the concept of similarity .

All of these methods utilise the counter-regulatory reaction to specific stimuli in order to use this as a therapeutically effective approach within the framework of attunement therapies. The concept of similarity is used as a therapeutic principle in different ways.

Containing is a direct communicative application of this concept.

Rebound effects of conventional pharmaceuticals

A separate analysis appears useful for conventional drug therapy, in which regulative effects are described as rebound or paradoxical drug reactions. From an epistemological perspective, these also provide confirmatory evidence for the principle of similarity in therapy, even if not intended.

• Rebound - The reversal of a reaction to the withdrawal of a stimulus
• Rebound effect - The increased production of negative symptoms when the effect of a drug has worn off or the patient no longer responds to the drug.
• Paradoxical reaction - When a drug causes a rebound effect, the condition that was treated with the drug may return even stronger when the drug is discontinued or loses its effect.

The sufferer experiences the same symptoms that they had expected to disappear when taking medication. The opposite or contrary effect to the symptoms of the disease and physiological manifestations often occur with greater intensity and/or frequency.

Explanatory models for the rebound effect

"Overall, the rebound effect (paradoxical reaction) is the result of the organism's autonomous attempts to return to its basic state (homeostasis) after it has been altered by the primary effect of an administered drug (medication).

Since a characteristic of living beings is their ability to maintain a constant internal environment through autoregulatory physiological processes, homeostatic mechanisms are present at all levels of biological organisation, from simple cellular mechanisms to the most complex psychological functions." (Teixeira, 2013, p. 630, author's translation)

Based on the research of Varela and Maturana, the term homeostasis is replaced below by homeodynamics, which more comprehensively describes the ability to adapt to changing conditions and maintain a dynamic equilibrium.

As has been demonstrated in clinical and experimental pharmacology, the rebound effect therefore has some special characteristics (Teixeira, 2013) :

• It occurs particularly in susceptible individuals (1 /1000),
• it is independent of the type of medication used or the person's illness (symptoms),
• It occurs after partial or complete discontinuation of the medication, depending on the individual characteristics,
• it promotes a clinical condition that is opposite to the primary effect of the drug,
• the symptoms it causes are more intense than those before treatment and
• the extent of the effect is proportional to the primary effect of the drug.

Clinically well-documented rebound effects have so far been found for the following active pharmaceutical ingredients: (insert background paper)

• ASA and NSAIDs
• Bronchodilators
• Antidepressants
• Statins with paradoxical discontinuation syndrome
• Proton pump inhibitors (PPI)
• Bisphosphonates

Analysis of the Organon paragraphs on the rebound effect

Hahnemann's Organon also contains references to rebound effects to justify the simile concept in §§ 22-28 and § 52, §§ 54-60 (Hahnemann, 2017) . The connection was obviously clinically evident to Hahnemann and is supported by citations from other sources (see footnote to § 58):

§ 22 Two principles of medicinal action are to be distinguished, either remedies are chosen which can produce symptoms similar (homoeopathic) or opposite (antipathic) to the disease state, which is to be proved by empirical evidence.

§ 23 Opposite, antipathic, enantiopathic (Greek: directed against the suffering) prescriptions have at best a palliative and alleviating effect. The symptoms of the disease are not curatively influenced, but reappear after some time, to a greater degree.

§24 Therefore, the homeopathic prescription remains, in which the totality of all symptoms of the case of illness, its context of origin, as far as it is known, and all accompanying complaints are used for the choice of remedy.

§ 25 Empirical evidence shows that the most commonly chosen homeopathic remedies, based on the results of the provings, in potentised form and small amounts, induce curative responses.

§ 26 The homoeopathic principle requires that the therapeutic stimulus be sufficiently similar to the pathogenic affection and at the same time superior in intensity.

§ 27 The healing power of remedies is therefore based on their ability to trigger a physiological change of mood if they are sufficiently homoeopathically adapted to the individual case and the medicinal power is stronger than the disease-causing stimulus itself.

§ 28 The homeopathic principle is empirically demonstrable. A scientific theoretical explanation is of secondary importance in order to derive the empirically based premises and is therefore not necessary.

The model of "artificial disease" propagated by Hahnemann is not considered in this analysis. A discussion of this can be found in the section Hahnemann's model of disease (link).

§ 52 The homeopathic and allopathic[2] approaches are based on opposing, incompatible principles and cannot be combined arbitrarily in a single case of illness.

§ 54 The allopathic treatment concept defines diseases in a standardised way and therefore works with therapeutic schemes that are superordinate to the individual case. The basis for this are the respective determining theoretical guidelines for recognising disease, which consequently lead to different classifications of disease entities and are based less on empirical data.

§ 55 The primary effect of allopathic therapy is palliative, providing immediate relief and symptomatic relief.

§ 56 The antipathic methodology is based on Galen's doctrine of countering the opposite with the opposite. However, the alleviations triggered are only palliative. Particularly in the case of chronic illnesses that do not progress very quickly, they only lead to episodic feigned improvements, as they are only directed at a part of the symptoms.

§ 57 The procedure of prescribing an alleviating remedy or measure for a part of the symptoms is always based on the fact that a palliative effect is known for this particular symptomatology according to the contraria contrariis principle. All other symptoms of the case are not taken into account. Hahnemann gives several examples to illustrate this approach:

• Opiates for severe pain
• Laxatives for constipation
• Cold as an immediate measure for burns
• Warm baths in frosty weather
• Stimulants for states of weakness

§ 58 The allopathic use of medicines is purely symptomatic and is not aimed at treating the underlying long-term disorder or disease. Therefore, after phases of symptomatic improvement, such applications usually lead to aggravation of the entire disease, which is interpreted as malignancy of the event or as a new disease.

§ 59 Hahnemann gives many examples of rebound effects in different therapeutic situations:

• Coffee against daytime tiredness, first increased vigilance, then greater exhaustion and drowsiness
• Opiates for insomnia, first anaesthesia with loss of consciousness, followed by agitation and insomnia in the following nights
• Opiates for infectious diarrhoea, which lead to cessation due to intestinal paralysis, followed by increased diarrhoea
• Opiates for infectious chesty cough, which leads to feverish conditions and sweating in counter-regulation
• Cantharide tincture for bladder irritation in cases of urinary retention, which forces the bladder to empty and subsequently increases urinary retention
• The vicious circle of laxatives for constipation: the more constipation, the more laxatives, which leads to more constipation
• Stimulants for states of weakness, which lead to increased tiredness and exhaustion after a brief increase in vigilance
• Bitter substances and irritating spices for atrophic gastritis, which ultimately reduces gastric motility
• Frostiness due to warm baths, which first warm up and then cause more sensitivity to cold and freezing in the counter-regulation
• Cold for burns, which initially alleviates the pain but increases the inflammation in the counter-regulation and thus increases the tissue damage
• Chronic nasal mucosal swelling treated with mucosal irritants leads to increased mucosal swelling and nasal congestion after initial secretion
• High-dose electrical stimulation of paralysed extremities, which leads to increased destruction of muscle tissue with an increase in the paralysis pattern
• Bloodletting as a measure against congestion and palpitation, which increases these symptoms in counter-regulation
• Large doses of valerian in typhoid conditions, which ultimately increase total exhaustion and tend to increase the mortality rate, especially in patients treated in this way
• Digitalis for atrial fibrillation, which leads to weakness and death if the effect wears off and doses are increased carelessly

§ 60 To summarise, the antipathic use of medicines leads to increased counter-regulation with an increase in symptoms, which is usually countered by increasing the dose. However, the palliative effect diminishes over time and the overall disease situation worsens due to an increase in the same complaint or the appearance of other new and more severe symptoms. A cure of the original condition is not achieved.

Even if Hahnemann's examples are considered outdated in some places today or are far less dangerous due to better dosing, they impressively demonstrate the style of thinking and the consequences in the approach to paradoxical drug reactions.

From an epistemological perspective, it is precisely the fact that rebound effects have a regulative physiological basis and thus represent indirect evidence for the similie principle. Regardless of the nature of the measures over the centuries, they are seemingly timelessly valid, as becomes clear when compared to today's conventional medical therapeutic approaches

Literature analysis of homeopathic medicinal effects

A further analysis of the medicinal effect according to the concept of similarity can be carried out by a direct examination of the homeopathic hypotheses of medicinal effect. A detailed literature comparison of Hahnemann's statements with basic works of modern toxicology and pharmacotherapy of 56 plants was carried out as part of a dissertation (Boucsein, 1992) . The statements are organised into disease and symptom groups based on the ICD-10, the focus was on identifying:

• Consistent statements between Hahnemann and today
• Contradictory statements
• Statements by Hahnemann without correlations to the reference literature

Poisoning symptoms (high doses) and therapeutic indications with high and low doses were compared. The following definition was used as a starting point:

"If a plant produces a poisoning syndrome in high doses that corresponds to the symptoms it combats in low (therapeutic) doses, the therapeutic use of the plant against a corresponding symptom is by definition a use according to the principle of similarity (...).

If, on the other hand, a plant combats a symptom through an opposite effect, and retains the opposite effect even in higher, toxic doses, this is an application according to the principle of antagonism [antagonism principle; author's note]." (Boucsein, 1992, p. 582ff)

RESULT: "About 2/3 of the effects of the plants discussed were correctly described by Hahnemann, 1/3 of the indications cannot be correlated with the modern literature, and 4.5% of his observations are apparently based on incorrect observations." (Boucsein, 1992, p. 581) Hahnemann correctly predicted 30.7% of the indications, almost 68% of the indications were incorrect, and the proportion of incorrect statements was 1.14%. (Boucsein, 1992, p. 585)

The differences in the non-correlating symptoms are due to the fact that modern authors refer to an isolated description of acute intoxications and not to a complete list of all individual symptoms, which still occur days after the poisoning, but which are characteristic of the homeopathic materia medica. (Boucsein, 1992, p. 582 f.)

OVERALL RESULT OF THE ANALYSIS: Even according to modern toxicological-pharmacological criteria, Hahnemann's postulates based on the principle of similarity are statistically significant.

DISCUSSION: It turned out that almost half of the "conventional medical indications" of the plants investigated are homeopathic in the true sense of the word, "...because they are only understandable against the background of an application in the sense of the principle of similarity. In concrete terms, this means that, for example, a plant that produces diarrhoea in high doses is used therapeutically against diarrhoea. And this is not within the framework of the "outsider method" of homeopathy, but has been recognised for decades within the framework of "conventional medicine[3] (Boucsein, 1992, p. 592)

SUMMARY: This leads to several conclusions that are derived logically from the work:

Hahnemann can timelessly be considered a very good clinical observer, only 4.5% of his statements are based on false observations. The principle of similars as a prescription concept seems to have real significance, which can be explained as follows (Bouscein pp. 592-593):

1. About one third of Hahnemann's indications correspond with current therapeutic indications, which can be described as significant
2. Hahnemann was able to correctly derive predictions of as yet unknown therapeutic uses of medicinal plants from the concept of similarity in 23-31% of the observations.
3. The analysis of intoxication symptoms and therapeutic indications of various medicinal plants from current publications confirms that about half of the conventional indications are based on the homeopathic principle.

The high rate of correct predictions from the homeopathic remedy provings cannot simply be dismissed as a random reaction given the range of specific and consistent indications. Hahnemann's proposal to derive therapeutic indications from the poisoning picture based on the concept of similarity could serve to expand pharmacological knowledge of the medicinal effects of as yet unknown medicinal plants by means of broadly based provings.

Basic research on the principle of similarity

There is still a modest amount of basic research into the principle of similarity. This provides surprising results that make further and more comprehensive research appear worthwhile. The most impressive results of preclinical research in this area have so far been delivered by a Dutch working group.

In several studies from 1997 to 2009, the reactions of stress proteins under different conditions were investigated in a cellular model system. In these studies, cell clusters were stressed with a heat shock (HS). The post-treatment with low doses of a number of different stressors resulted in a higher survival rate of the damaged cells, the more the response to the respective secondary stressors corresponded to the spectrum of protective proteins (HSP) formed during the preceding heat shock. (F. Wiegant & Van Wijk, 2010)

Research on hormesis[4] by the same working group also shows in cell cultures that low-dose stressors administered before or after a harmful higher dose of the same stressor reduce the harmful effects of subsequent toxic doses (Van Wijk & Wiegant, 2010) . The results were last summarised in 2011 (F. A. C. Wiegant et al., 2011) .

Taken together, these studies support the simile principle at the cellular level and contribute to the understanding of how low-dose stress conditions influence the regulatory processes underlying self-healing.

In addition, the phenomenon of "symptom amplification", which is also observed at the cellular level, is discussed in connection with self-healing in the sense of postconditioning hormesis. The data support the hypothesis that low doses of toxic compounds under certain conditions can have beneficial effects in connection with the stimulation of endogenous cytoprotective mechanisms

Summary

The everyday examples mentioned, the application practice from naturopathy and conventional biomedicine including psychotherapy, the research on pharmacological rebound effects, the analysis of homeopathic drug action hypotheses and their use in everyday practice as well as the first results of basic research show that the simile principle is not a medical oddity of outdated 19th century ideas. Rather, it is an important approach to regulative therapies.

The special position of homeopathy can be understood as a consistently differentiated and systematic application of this concept in the prescription of remedies with an empirical background of verified drug reactions that has been growing for 220 years.

From a pragmatic point of view, the significance of the simile principle in homeopathy as a therapeutic concept for prescribing remedies is precisely what epistemologically describes and justifies the application practice in homeopathy.

A discussion that has been going on for over 200 years as to whether it is a rule, a principle or a law implements an unnecessary paradigmatic dispute that, as explained, is basically obsolete for understanding.

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[1] "In psychology, containment refers to the process by which one person (container) can absorb the emotions or affects of another person (containend), process them and return them in a way that is bearable for the containend. The concept of containment was originally developed by the British psychoanalyst Wilfred R. Bion (2001), according to whom containment is a fundamental function of the mother-child relationship, because the mother takes in her child's feelings without being overwhelmed by them, then processes them internally and returns them to the child in a way that the child can understand and cope with." (Stangl, 2025; author’s transl.)

[2] Allopathy: therapeutic principles that counteract the condition, e.g. fever reducer in the event of a rise in temperature

[3] As the term conventional medicine is often used pejoratively in discussions of alternative medicine, it is better to use the term conventional medicine. Author's note].

[4] Hormesis describes a multiphase dose-response relationship. Low doses of a stressor have a stimulating effect, while higher doses have either inhibitory or toxic effects.

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Sources and References

• Boucsein, H.-U. (1992). Die Begründung des Ähnlichkeitsprinzips durch Hahnemann aus heutiger Sicht: Aussagen aus Samuel Hahnemanns „Versuch über ein neues Princip ...“ (1796) im Vergleich mit modernen Autoren und ein Versuch der Überprüfung des Ähnlichkeitsprinzips. Königshausen und Neumann.
• Hahnemann, S. (1796). Versuch über ein neues Prinzip zur Auffindung der Heilkräfte der Arzneisubstanzen. Hufelands Journal der practischen Arzneykunde, 2, 391–439.
• Hahnemann, S. (2017). Organon der Heilkunst (6. Aufl.). Hahnemann Institut für homöopathische Dokumentation. https://archive.org/details/organon-der-heilkunst
• Jütte, R. (1997). 200 Jahre Simile-Prinzip: Magie, Medizin, Metapher. Allgemeine Homöopathische Zeitung, 242(01), 3–16. https://doi.org/10.1055/s-2006-936588
• Stangl, W. (2025). Containment. In Online Lexikon für Psychologie und Pädagogik. https://lexikon.stangl.eu/37074/containment
• Teixeira, M. Z. (2013). Rebound effects of modern drugs: Serious adverse events unknown by health professionals. Revista Da Associação Médica Brasileira (English Edition), 59(6), 629–638. https://doi.org/10.1016/S2255-4823(13)70530-7
• Van Wijk, R., & Wiegant, F. (2010). Postconditioning hormesis and the homeopathic Similia principle: Molecular aspects. Human & Experimental Toxicology, 29(7), 561–565. https://doi.org/10.1177/0960327110369860
• Wiegant, F. A. C., Prins, H. A. B., & Van Wijk, R. (2011). Postconditioning Hormesis Put in Perspective: An Overview of Experimental and Clinical Studies. Dose-Response, 9(2), dose-response.10-004.Wiegant. https://doi.org/10.2203/dose-response.10-004.Wiegant
• Wiegant, F., & Van Wijk, R. (2010). The similia principle: Results obtained in a cellular model system. Homeopathy, 99(1), 3–14. https://doi.org/10.1016/j.homp.2009.10.002

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Authors: glt | Rev.: gbh, mnr, sfm, smi | Ed.: pz | Last modified Apr. 10, 2025