Observational studies with preparations of St. John's wort have recorded an incidence of adverse events (AE) among those treated of between 1 and 3%. This is some ten times less than with synthetic antidepressants. The most common adverse events (1 per 300000 treated cases) among the spontaneous reports in the official register concern reactions of the skin exposed to light. Investigations in volunteers have shown that the threshold dose for an increased risk of photosensitisation is about 2-4 g/day of a usual commercial extract (equivalent to approximately 5-10 mg of the hypericin that causes the phenomenon). In view of the newly observed side effects and interactions, the following additional restrictions on use appear justified: as with all preparations in this group of indications, hypericum preparations must not be taken at the same time as other antidepressants. If co-medication with coumarin-type anticoagulants is unavoidable, it must only be undertaken provided the physician closely monitors clotting parameters. Co-medication with ciclosporin and indinavir, and for the time being, other protease inhibitors used in anti-HIV treatment, is absolutely contraindicated. Without exception, all preparations of St. John's wort must only be available through pharmacies.