This is the second of two papers which review issues concerning complementary medicines. The first reviewed the extent of use of complementary medicines, and issues related to the regulation and pharmaceutical quality of these products; the second considers evidence for the efficacy of several well-known complementary medicines, and discusses complementary-medicines pharmacovigilance. The term complementary medicines describes a range of pharmaceutical-type preparations, including herbal medicines, homoeopathic remedies, essential oils and dietary supplements, which mainly sit outside conventional medicine. The use of complementary medicines is a popular healthcare approach in the UK, and there are signs that the use of such products is continuing to increase. Patients and the public use complementary medicines for health maintenance, for the treatment or prevention of minor ailments, and also for serious, chronic illnesses. There is a growing body of evidence from randomized controlled trials and systematic reviews to support the efficacy of certain herbal extracts and dietary supplements in particular conditions. However, many other preparations remain untested. Strictly speaking, evidence of efficacy (and safety) for herbal medicines should be considered to be extract specific. Pharmacovigilance for complementary medicines is in its infancy. Data are lacking in several areas relevant to safety. Standard pharmacovigilance tools have additional limitations when applied to investigating safety concerns with complementary medicines.