St John's Wort: Evidence, Product Differences and Interactions

St John’s wort is a yellow-flowered plant. Supplements commonly use preparations of the herb. A study of a defined extract is evidence about that preparation and setting; it should not be read as proof that every tea, tincture or capsule has the same effect.^{See reference 1,See reference 2}

Preparations differ in their constituents, including hypericin and hyperforin. The systematic review found variation across extracts as well as across study results. A label’s milligrams of herb and milligrams of extract are therefore not a ready-made equivalence calculation.^{See reference 2,See reference 4}

A systematic review combines trials with different participants, extracts and methods. The 2016 review included 35 studies and 6,993 participants, but the studies were not one uniform experiment. Its conclusions were limited by inconsistent results, sparse evidence in severe depression and incomplete assessment of adverse effects.^{See reference 2}

In the 340-participant JAMA trial, neither St John’s wort nor sertraline outperformed placebo on the two primary outcomes. Sertraline did perform better on one secondary measure. This trial cannot establish that antidepressants as a class are ineffective; it illustrates why the product, population and chosen outcome need to stay with the result.^{See reference 6}

For a reader, the practical question is not simply whether a trial exists. Ask whether it studied the same preparation, severity of illness, outcome and duration as the claim being made. A supplement claim that omits these details is harder to assess.

St John’s wort can increase the activity of systems that process or transport medicines. For some medicines, this reduces the amount circulating in the body and weakens their effect. The TGA also warns that levels of interacting medicines can rise when St John’s wort is stopped. Starting, stopping or switching preparations can therefore matter.^{See reference 4}

A different interaction involves medicines that affect serotonin. Combining effects can increase serotonin-related adverse reactions. “It lowers drug levels” is not a sufficient explanation for every interaction; some combinations can instead increase harmful effects.^{See reference 1,See reference 4}

Reported adverse effects include digestive upset, dizziness, sleep problems and restlessness. Sun-related skin reactions can occur, particularly with large oral amounts or topical use. Pregnancy may be unsafe, and adverse effects have been reported in breastfed infants.^{See reference 1}

NCCIH also describes reports of worsening symptoms in people with bipolar disorder or schizophrenia. Depression can be a serious illness; an herb should not replace an assessment or delay needed care. This guide does not select a depression treatment or a supplement dose.^{See reference 3}

If St John’s wort is already being used with medicines, contact the prescribing team or pharmacist for an individual plan before making changes. The interaction review needs both the medicines and the supplement history, including recent changes in product.^{See reference 4}