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St. John's Wort for depression: strong evidence, serious interactions
St. John's Wort (Hypericum perforatum) is the most clinically studied herbal medicine for depression. In Germany, where it is licensed as a treatment for mild to moderate depression, it outsells Prozac. In most English-speaking countries it sits as an unregulated supplement, which means most people either misuse it or have no idea how well it has been tested.
The evidence base
A 2008 Cochrane Review analyzed 29 randomized trials involving 5,489 patients: St. John's Wort was significantly more effective than placebo for mild to moderate depression and similarly effective to standard antidepressants with fewer side effects. A 2016 systematic review in the Journal of Affective Disorders confirmed these conclusions and noted significantly lower dropout rates due to adverse effects compared to pharmaceutical antidepressants. The evidence does not support use for severe depression. The positive trials are specifically for mild to moderate presentations.
Timeline: Like pharmaceutical antidepressants, St. John's Wort takes four to eight weeks to produce full effects. Consistent use over two months is necessary to evaluate whether it works.
The drug interactions: not optional reading
St. John's Wort induces cytochrome P450 enzymes (CYP3A4, CYP2C9) and the drug transporter P-glycoprotein, speeding up the metabolism of many medications and reducing their blood levels. Medications significantly affected: oral contraceptives (documented pregnancy risk), HIV antiretrovirals (documented treatment failure), cyclosporine/transplant antirejection (documented rejection episodes), warfarin (reduced anticoagulation), some SSRIs (risk of serotonin syndrome), certain statins and anticonvulsants. These are confirmed by case reports and controlled studies. If you are on any prescription medication, check interactions before taking St. John's Wort. A pharmacist can do this in five minutes.
Appropriate use
For mild to moderate low mood or seasonal affective disorder in someone not on interacting medications: a reasonable option with strong evidence. Standard dose: 300 mg three times daily of extract standardized to 0.3% hypericin. Not appropriate as a substitute for professional mental health care. St. John's Wort is real medicine with real benefits and real risks.
How St. John's Wort compares to antidepressants
The 2008 Cochrane Review found St. John's Wort comparably effective to standard antidepressants for mild to moderate depression, with a significantly better side effect profile. The dropout rate due to adverse effects was notably lower than in the pharmaceutical arms of included trials. Common side effects with St. John's Wort: photosensitivity, mild gastrointestinal upset, dry mouth, and dizziness. The sexual side effects common with SSRIs, the weight changes, and the emotional blunting appear at much lower rates. This does not make it superior in all respects, and it does not make it appropriate for severe depression. But for mild to moderate presentations in someone not on interacting medications, the evidence-based case is stronger than most people realize.
Quality and standardization
St. John's Wort is standardized to 0.3% hypericin in most research. Hypericin is an easy-to-measure marker compound, but there is ongoing debate about whether hyperforin is actually the more therapeutically important compound. Products standardized to hyperforin content (typically 3-5%) may be more consistently effective. Look for products that specify their standardization clearly. A product that just says "St. John's Wort extract" without specifying the marker and percentage does not give you enough information. Herb Pharm, Gaia Herbs, and Nature's Way have produced consistently quality preparations.
Frequently asked questions
How do I know if it is working? Like pharmaceutical antidepressants, the full effect takes four to eight weeks. At two weeks, some people notice improved sleep. At four weeks, energy and motivation often improve before mood fully lifts. If there is no improvement after eight weeks at full therapeutic dose, the herb is unlikely to be effective for you.
Can I stop taking it suddenly? St. John's Wort does not appear to cause significant discontinuation syndrome. Tapering over one to two weeks is still a reasonable approach but abrupt discontinuation is unlikely to cause the acute withdrawal effects seen with some SSRIs. See also: how to source herbal supplements responsibly.
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