St John’s wort (Hypericum perforatum) is a perennial herb that can be used as a complementary medicine. It is commonly used, often as self-medication, for the treatment of depression. St John’s wort is so named because the plant opens its yellow flowers in the northern hemisphere around the feast day of St John the Baptist in late June. Wort is an old English word for plant.

Uses for St John’s wort

St John’s wort is available without a prescription, either alone or as part of a preparation with other ingredients. It is available as tablets, capsules, oral liquid and as ointment.

St John’s wort has been used in the treatment of several conditions, including:

  • depression;
  • anxiety;
  • premenstrual syndrome;
  • stress;
  • sleep disturbance;
  • sciatica pain; and
  • minor skin wounds and dermatitis (ointment).

There is a lack of evidence from clinical trials supporting the effectiveness of St John’s wort for many of these conditions.

There is some evidence showing that St John’s wort may be effective for the treatment of mild depression. It’s thought that the beneficial effects of St John’s wort stem from its effect on neurotransmitters (such as serotonin) in the brain that are linked to anxiety and depression.

Side effects

Like other herbal preparations and medicines, St John’s wort can cause side effects, with some users complaining of:

  • dry mouth;
  • dizziness;
  • restlessness;
  • increased sensitivity to sunlight (photosensitisation);
  • gastrointestinal symptoms;
  • sexual dysfunction;
  • headache; and
  • fatigue.

Allergic reactions have also been reported.

The safety of St John’s wort for use during pregnancy and breast feeding has not been established.

Interactions with other medicines

In Australia, St John’s wort is freely available, but preparations are regulated by the Therapeutic Goods Administration (TGA), which has warned that the strength of active ingredients may vary between preparations and that drug interactions are also possible with other medicines.

Some of the interactions may take the form of the St John’s wort boosting the effect of the other medicine, which then increases the risk of adverse reactions from that medicine. Another effect St John’s wort may have is to increase the breakdown of other medicines, thus reducing their concentration in the blood and hence their effect.

Some of the drugs that St John’s wort interacts with include:

  • antidepressants;
  • HIV medicines;
  • medicines that modify the immune system that are often used in people who have had organ transplants (e.g. cyclosporin, tacrolimus);
  • warfarin (a blood thinning agent);
  • certain medicines used in the treatment of heart disease (e.g. digoxin, nifedipine, verapamil);
  • certain cholesterol-lowering medicines (e.g. atorvastatin, simvastatin);
  • some medicines for type 2 diabetes (e.g. gliclazide);
  • anticonvulsants used in the treatment of epilepsy;
  • the contraceptive pill; and
  • migraine treatments.


St John’s wort may not be suitable for everyone. Always advise your doctor or health professional if you are already taking, or intending to take, a complementary medicine or herbal preparation.

St John’s wort should not be used if you are pregnant or breast feeding.

Your doctor or pharmacist will be able to advise you if St John’s wort is suitable for you (taking into account your medical history). They will also be able to tell you if St John’s wort interacts with any medicines you are taking.