Potential Side Effects of St. John’s Wort

While St. John’s wort is well-tolerated with minimal side effects, there are counter-indicated drug-drug interactions and potentially adverse photosensitive reactions

General Safety and Side Effects

dreamstime xxl 6431899 smA European drug-monitoring study of 3250 patients revealed an overall adverse drug reaction incidence of 2.4% for the clinical use of Hypericum extract in the treatment of depression (Woelk et al., 1994).   The most commonly reported side effects were gastrointestinal irritations (0.6%), allergic reactions (0.5%), fatigue (0.4%), and restlessness (0.3%).

A meta-analytic review concluded that when side effects do occur, they are generally mild, transient, and similar to placebo (Linde et al., 1996).

Drug-Drug Interactions

More recently, scientists have reported in vivo drug interactions between St. John’s wort extracts and protease inhibitors in HIV patients, and between SJW extracts and cyclosporine in heart transplant patients (Ernst, 1999).

There is a potential for drug-drug interactions between St John's wort and certain prescribed medicines (including warfarin, cyclosporine, theophylline, digoxin, HIV protease inhibitors, anticonvulsants, selective serotonin reuptake inhibitors, triptans, oral contraceptives).  Patients taking these medicines are advised to stop taking St John's wort.  

Generally professional advice should be sought in these cases as dose adjustment of conventional treatment may be necessary. Learn more


Light therapy combined with Hypericum extracts may increase the risk of phototoxicity in light skinned patients.  This photosensitivity is more likely to occur in St. John’s wort extracts containing hypericin. Learn more


  • Ernst E. (1999). Second thoughts about safety of St John's Wort. Lancet 354:2014-2016.
  • Linde K, Ramirez G, Mulrow C, Pauls M, Weidenhammer W and Melchart D. (1996). St. John’s wort for depression  -- an overview and meta-analysis of randomized clinical trials.Br Med J 313: 253-258.
  • Woelk H, Burkard G and Grunwald J. (1994). Benefits and Risks of the Hypericum Extract. LI 160: Drug Monitoring Study with 3250 Patients. J Geriatr Psychiatry Neurol 7 (Suppl 1): 34-38.