St. John’s wort

St. John's wort is a plant extract taken mainly for low mood. Human trials support some benefit in mild to moderate depressive symptoms, but its extensive interactions with prescription medicines are the dominant practical issue and the reason clinicians frequently advise against it.

Products are extracts of the flowering tops, usually standardised to hypericin or hyperforin. Hyperforin content drives the interaction potential and varies between products, so two extracts with the same label weight may behave very differently.

Constituents appear to increase the availability of serotonin, noradrenaline and dopamine in the brain, which is the proposed basis for mood effects.

Systematic reviews of randomised trials in mild to moderate depression find benefit over placebo and comparable short-term outcomes to some standard antidepressants with fewer reported side effects. Evidence is weaker for severe depression, and trial preparations differ enough that results do not transfer automatically between products.

Laboratory studies characterise monoamine reuptake inhibition by hyperforin and strong induction of drug-metabolising enzymes in hepatocyte and receptor models.

Evidence gap: Non-human evidence. It explains both the proposed benefit and the interaction risk; it does not establish clinical effectiveness.

This is the critical section. St. John's wort speeds up the breakdown of many medicines, lowering their levels and potentially causing treatment failure — including unintended pregnancy with hormonal contraception and organ rejection with transplant medicines. Combined with serotonergic drugs it can instead cause excessive serotonin effects.

Common effects include stomach upset, restlessness, sleep disturbance, dry mouth and increased sensitivity to sunlight. The serious risks are interaction-driven: loss of contraceptive protection, transplant rejection, reduced HIV or cancer treatment effectiveness, and serotonin syndrome with other serotonergic medicines. It may trigger mania in people with bipolar disorder, should not be combined with antidepressants except under specialist advice, and should be disclosed before surgery. It is not recommended in pregnancy or breastfeeding. Depression that is worsening, or any thoughts of self-harm, needs urgent professional care rather than a supplement.

Standardised extracts in capsules or tablets are the researched form; teas and tinctures are not equivalent.

For depressive symptoms, established options include psychological therapy, structured exercise, sleep and alcohol review, and prescribed antidepressants where indicated. St. John's wort is not a substitute for assessment, and it is a poor fit for anyone taking regular medicines.

Educational example: a person using a hormonal contraceptive starts St. John's wort for low mood and becomes pregnant; another stops it suddenly while on a transplant medicine and drug levels rise. Both illustrate that the risk lies in the interaction, in both directions. Questions for a clinician or pharmacist: does this affect any of my medicines, and what should change if I start or stop it? Ethically, marketing as a gentle natural alternative understates a genuinely high interaction burden, and self-treating significant depression can delay effective care.