Background  Homeopathy is a system of complementary and alternative medicine based on a belief that a malady can be treated by the administration of an extreme dilution of an agent thought to cause the physical signs of that malady. Homeopathy enjoys popular support from the general public and advocates of alternative medicine, but most large‐scale clinical trials show no homeopathy to be no more effective than placebo treatment.

Objectives  To explore the chemical and physical plausibility of homeopathic treatments.

Methods  Homeopathic claims were put into a physical context and analysed using the laws of basic physics and chemistry.

Results  Through the laws of physics, homeopathic medicines appear to have zero chance of containing any biologically active component. Evidence from physical chemistry also rules out the plausibility of mechanisms such as water memory.

Conclusions  The proposed mechanisms of homeopathy are shown to be implausible when analysed from a physical and chemical perspective, and thus it is of no surprise that the biological effects of homeopathy cannot be measured in large‐scale clinical trials.