Homeopathy is based on the principle that you can treat ‘like with like’, that is, a substance which causes symptoms when taken in large doses, can be used in small amounts to treat similar symptoms. For example, drinking too much coffee can cause sleeplessness and agitation, so according to this principle, when made into a homeopathic medicine, it could be used to treat people with these symptoms. This concept is sometimes used in conventional medicine, for example, the stimulant Ritalin is used to treat patients with ADHD, or small doses of allergens such as pollen are sometimes used to de-sensitise allergic patients.