St John's Wort Side Effects

Compared to conventional antidepressants, side effects to taking St John's wort are generally well tolerated.

However, a more natural product does not mean it's without side effects. In many cases, St John's wort products contain unnatural, synthesized versions of the active ingredient.

In such cases, the "it's natural so it must be safe", argument does not fare so well. Although rare, there are possible dangers of St John's wort which should be considered.

To put these precautions into perspective, studies have shown that the sides effects of St John's wort are no worse than placebo [1] and are usually mild in nature.

Studies indicate that only 1-3% of people taking St John's wort experience any of the following side effects [6]:

  • confusion
  • dizziness
  • gastrointestinal symptoms – stomach upset, diarrhea, nausea
  • fatigue
  • tiredness
  • dry mouth
  • allergic skin reactions
  • sexual dysfunction – e.g. erectile dysfunction, orgasmic delay

Less common St John's wort side effects include photosensitization and serotonin syndrome. These are discussed in the section, 'Dangers of St John's wort'.

The Interaction Of St John's Wort With Other Drugs & Medicines  

St John's wort is freely available to buy over the counter in many countries.

However, in some countries such as Ireland & Germany it is available by prescription only. This is largely because St John's wort may cause decreased concentrations and effectiveness of existing medication.

A precription requirement means a doctor is sought first; potential problems and dangers of St John's wort can be assessed.

St John's wort may decrease the concentrations and effectiveness of:

  • antiretrovirals – e.g. some drugs used to treat HIV such as Indinavir (trade name: Crixivan)
  • benzodiazepines – group of psychoactive drugs, often used as a sedative
  • hormonal contraception – e.g. 'the pill' - reduced effectiveness a side effect of using St John's wort and birth control
  • immunosuppressants – e.g. Cyclosporine
  • anticonvulsants – used to treat epilepsy
  • digoxin (digitalis) – used to treat various heart conditions; strengthens heart muscle contractions

In addition to reducing the effectiveness of certain drugs, St John's wort may prolong the effects of sleeping pills and anaesthetics.