Dr Fred Kavalier answers your health question:

St John's wort is produced from a plant of the same name in the Hypericum family. It is not a licensed drug in the UK, but it is widely available as an over-the-counter treatment for depression. It has been studied extensively and it does seem to have genuine antidepressant properties. But just because it is a natural plant remedy doesn't mean that it can't interact with other medicines. The British National Formulary lists 26 different drugs and groups of drugs that have an interaction with St John's wort. Many of these are interactions that probably won't make much difference, but a few are potentially important. If you are taking drugs for HIV infection, you must be particularly careful with St John's wort. There are quite a few anti-HIV drugs that are made less effective by the presence of St John's wort. A drug called ciclosporin, used for people who have had kidney transplants, also interacts with St John's wort in a serious way. Some drugs that are used in epilepsy and migraine can be affected by St John's wort. Perhaps most important, St John's wort can have an effect on blood levels of the SSRI family of antidepressants, which includes Prozac and Seroxat. Taking St John's wort with these is not recommended. And finally, St John's wort can effect the oestrogen levels of people on the contraceptive pill, possibly making the contraceptives less effective. The full list of interactions is available on the British National Formulary website: www.bnf.org. You have to register the use the website, but it is freely available to all and is a good source of information on all prescribed drugs. Regarding alcohol, it's best to drink only small amounts, or none at all, if you are taking St John's wort.

Please mail your questions for Dr Fred to health@independent.co.uk. He regrets that he is unable to respond personally to questions.