Research dossier
Clinical research on St. John's Wort
9 trials reviewed across 3 indications.
Strongest evidence
Mild-to-moderate depression and low mood
Mechanism
Hyperforin (and to a lesser extent hypericin) inhibits reuptake of serotonin, norepinephrine, and dopamine and modulates other neurotransmitter systems — a broad, antidepressant-like profile. The same serotonergic activity that helps mood is what creates serotonin-syndrome risk with other serotonergic drugs.
This is one of the few herbals that genuinely works for its headline claim. The Cochrane review of 29 RCTs (5,489 patients) found standardized extracts comparable to SSRIs for mild-to-moderate depression, with fewer side effects. But the US HDTSG trial was null for moderately severe depression (sertraline also missed), so the honest boundary is: helpful for mild-to-moderate, unproven for severe.
Evidence supports mild-to-moderate depression with a STANDARDIZED extract (WS 5570, LI 160). Not for severe or treatment-resistant depression. Never combine with an SSRI/SNRI, triptan, or other serotonergic drug without medical supervision — serotonin syndrome risk.
Trials cited
Cochrane review — St. John's Wort for major depression
positive · Systematic review
Linde et al., 2008, Cochrane Database of Systematic Reviewsn=5489The strongest synthesis for St. John's Wort: 29 RCTs in 5,489 patients found standardized hypericum extracts superior to placebo (response RR 1.28 in larger trials) and as effective as standard antidepressants (RR vs SSRIs 1.00), with markedly fewer dropouts for side effects.
Effect was larger in trials from German-speaking countries and in less severely depressed populations. Extracts and standardization varied; results apply to specific standardized products, not unstandardized retail bottles.
WS 5570 in mild-to-moderate depression (placebo-controlled)
positive · RCT
Lecrubier et al., 2002, American Journal of Psychiatryn=375Double-blind RCT in 375 outpatients with mild-to-moderate depression. WS 5570 at 900 mg/day produced a significantly greater HAM-D reduction than placebo over 6 weeks, with response and remission rates favoring hypericum.
Manufacturer (Dr. Willmar Schwabe) developed the WS 5570 extract. Confined to mild-to-moderate severity — does not speak to severe depression.
WS 5570 vs paroxetine (non-inferiority trial)
positive · RCT
Szegedi et al., 2005, BMJn=251Double-blind, double-dummy non-inferiority trial in 251 patients. WS 5570 was at least as effective as the SSRI paroxetine for moderate-to-severe depression and was better tolerated (fewer adverse events).
Manufacturer-sponsored, single-country (Germany), 6-week duration. 'Moderate-to-severe' here was defined by HAM-D ≥ 22, not the same as the treatment-resistant severe population in the null HDTSG trial.
HDTSG — St. John's Wort for moderately severe depression
Null · RCT
Hypericum Depression Trial Study Group, 2002, JAMAn=340The pivotal US NIH trial. In 340 patients with moderately severe depression, St. John's Wort was no better than placebo. Notably, the active comparator sertraline also failed to beat placebo on the primary endpoint — a 'failed trial' that limits how much it disproves hypericum, but it remains the key null result against severe-depression claims.
Because sertraline (a proven SSRI) also missed, the trial is widely read as underpowered or insensitive rather than proof hypericum is inert. Still, no credible evidence supports St. John's Wort for severe depression.
Photosensitivity (a risk, not a benefit)
Mechanism
Hypericin is a photosensitizing pigment. At high intake or with fair skin and strong sun exposure it can lower the threshold for sunburn and phototoxic skin reactions.
Listed as a risk, not a benefit. St. John's Wort does nothing good for skin — hypericin's photosensitivity means users (especially fair-skinned, high-dose, or sunbed users) can burn more easily. Use sun protection and avoid tanning beds while taking it.
Greatest concern at high doses, in fair-skinned individuals, and with intense UV exposure. Not a dermatological treatment.
Cardiac and immunosuppressant drug interactions (a risk, not a benefit)
Mechanism
St. John's Wort is a potent activator of the pregnane-X receptor, inducing CYP3A4, CYP2C9, and the P-glycoprotein transporter. This accelerates clearance of many drugs, dropping their blood levels — including digoxin and the transplant immunosuppressants ciclosporin and tacrolimus.
A risk entry. It lowers digoxin exposure (~25%) and has caused biopsy-confirmed transplant rejection by collapsing ciclosporin levels. For narrow-therapeutic-index cardiac and transplant drugs, this is potentially life-threatening, not therapeutic.
Absolutely contraindicated in transplant recipients and anyone on digoxin, warfarin, or other narrow-index medications unless explicitly cleared by the prescriber.
St. John's Wort lowers digoxin exposure
positive · RCT
Johne et al., 1999, Clinical Pharmacology & Therapeuticsn=25Co-administration cut digoxin Cmax ~26% and AUC ~25% via P-glycoprotein induction. For a narrow-therapeutic-index cardiac drug, this magnitude of reduction can produce loss of rate or rhythm control.
Healthy-volunteer pharmacokinetic study. 'Positive' means the interaction was demonstrated; clinically it is a loss of drug efficacy, not a benefit.
Acute heart transplant rejection from St. John's Wort
positive · Observational
Ruschitzka et al., 2000, The Lancetn=2Two previously stable heart transplant patients developed acute, biopsy-confirmed rejection after starting St. John's Wort, which cut their ciclosporin levels below the therapeutic range. Levels recovered when they stopped it. The interaction is now a textbook contraindication for transplant patients.
Case series (n=2), but the mechanism (CYP3A4 and P-glycoprotein induction lowering immunosuppressant levels) is well established and corroborated by additional kidney, liver, and pancreas rejection reports.
2 forms of St. John's Wort compared
St. John's Wort standardized to 0.3% hypericin
Standardized whole-plant hydroalcoholic extract
Best forThe traditional standardization marker used in many depression trialsHypericin standardization (typically 0.3%) is the older convention. Many of the positive depression trials used extracts standardized this way (e.g. LI 160). The active antidepressant constituent is now thought to be hyperforin more than hypericin, so hypericin content alone does not guarantee potency.
WS 5570, LI 160
St. John's Wort standardized to hyperforin (WS 5570 / LI 160)
Standardized hydroalcoholic extract; hyperforin is the principal active
Best forMild-to-moderate depression — the best-studied formWS 5570 (Dr. Willmar Schwabe) and LI 160 are the extracts behind most positive trials. Hyperforin is both the antidepressant driver AND the strongest enzyme inducer — high-hyperforin extracts carry the greatest drug-interaction risk. There is no 'interaction-free' standardized form that still works for depression.
stress600–1200 mg
Are you deficient? Symptoms, risk groups, lab tests
St. John's Wort is a medicinal herb, not an essential nutrient — there is no deficiency state. It is used for its pharmacological effect on mood, not to correct a dietary shortfall.
Common symptoms
- Not applicable — St. John's Wort is not an essential nutrient and has no deficiency syndrome
Side effects and drug interactions
Side effects
Photosensitivity (phototoxic skin reactions)
Uncommon · More likely at higher intakes; reported across typical antidepressant doses
Hypericin is a photosensitizer. Increased sunburn risk and phototoxic skin/eye reactions can occur, especially in fair-skinned people, at high doses, or with strong UV exposure and tanning beds.
Serotonin syndrome
Severe
Because St. John's Wort raises serotonergic tone, combining it with SSRIs, SNRIs, triptans, tramadol, MAOIs, or other serotonergic agents can cause serotonin syndrome — agitation, tremor, sweating, hyperthermia, and, rarely, life-threatening instability.
GI upset, dizziness, dry mouth, fatigue
Common
The most common direct side effects. Generally milder and less frequent than with prescription antidepressants — a key reason it is studied as a better-tolerated option.
Withdrawal of co-medication effect
Uncommon
When a stable patient adds or stops St. John's Wort, the blood levels of their other medications can swing as enzyme induction ramps up or wears off — a hidden cause of loss of control or unexpected toxicity.
Impaired glucose tolerance
Uncommon
St. John's Wort may impair glucose control and insulin secretion. In healthy volunteers, 2-hour glucose rose about 40% after 21 days and stayed elevated for 6 weeks after stopping. People with diabetes, prediabetes, or metabolic risk should monitor blood glucose and consult their prescriber.
Mania or mood elevation
Uncommon
As a serotonergic agent, St. John's Wort has been associated with induction of mania or hypomania. People with bipolar disorder or a history of mood disorders should not use it without consulting their prescriber.
Hyponatremia (SIADH)
Rare
Rare case reports have documented SIADH (inappropriate antidiuretic hormone secretion) leading to low blood sodium. Symptoms include nausea, headache, confusion, and lethargy — seek medical attention if these develop.
Male reproductive effects (in vitro)
Rare
In vitro studies show potent inhibition of sperm motility at high concentrations. Human clinical relevance is unclear — no in vivo human reproductive studies exist — but men trying to conceive may wish to discuss use with their prescriber.
Drug interactions
Reduces nutrient status
oral and other hormonal contraceptives (ethinyl estradiol, norethindrone, progestins)CYP3A4 induction accelerates clearance of contraceptive hormones, causing breakthrough bleeding and breakthrough ovulation.
Do not rely on hormonal contraception alone while taking St. John's Wort. Unintended pregnancies have been reported. Use a backup or alternative method and consult your prescriber.
Reduces nutrient status
ciclosporin (cyclosporine)tacrolimussirolimusCYP3A4 and P-glycoprotein induction collapses immunosuppressant blood levels, allowing the immune system to attack the graft.
Absolutely contraindicated in organ-transplant recipients. Biopsy-confirmed acute rejection has occurred. Never combine.
Reduces nutrient status
HIV antiretrovirals (protease inhibitors such as indinavir; many NNRTIs)CYP3A4 induction can cut antiretroviral exposure by half or more, risking viral rebound and drug resistance.
Contraindicated with most antiretroviral regimens. Indinavir AUC fell 57% in study. Do not combine with HIV therapy.
Reduces nutrient status
warfarindirect oral anticoagulantsInduction of CYP2C9 (warfarin) and related pathways reduces anticoagulant effect, lowering INR and raising clot risk.
Avoid. If unavoidable, INR/anticoagulation must be monitored closely by the prescriber, with re-checks again on stopping the herb.
Reduces nutrient status
chemotherapy (irinotecan, imatinib, and other CYP3A4-metabolized agents)CYP3A4 induction lowers active drug or metabolite levels — SN-38 (irinotecan) fell 42%, imatinib exposure fell ~30%.
Contraindicated during chemotherapy. Cancer patients must disclose all supplements to their oncology team.
Reduces nutrient status
digoxinstatins (simvastatin, atorvastatin)certain calcium-channel blockersP-glycoprotein and CYP3A4 induction lowers blood levels of these cardiovascular drugs, reducing their effect.
Avoid in patients on digoxin or other narrow-therapeutic-index cardiac drugs unless monitored. Discuss with the prescriber.
Combined-effect risk
SSRIs/SNRIstriptanstramadolMAOIsother serotonergic agentsAdditive serotonergic activity raises the risk of serotonin syndrome.
Do not combine with prescription antidepressants or migraine triptans without medical supervision. This is a dangerous overlap, not a synergy.
Combined-effect risk
photosensitizing agents (systemic aminolevulinic acid and others)St. John's Wort enhances the phototoxic effect of aminolevulinic acid (used in some skin and cancer treatments) and other photosensitizing drugs.
Avoid combining with topical or systemic photosensitizing therapies. Inform your oncologist or dermatologist if you take St. John's Wort.
Reduces nutrient status
CYP2E1 substratesSt. John's Wort also induces CYP2E1, a minor enzyme — adding to its broad enzyme-inducing profile, though the clinical impact is less established than its CYP3A4 induction.
A further reason to review every medication with a pharmacist before starting St. John's Wort.
Other critical caveats
- St. John's Wort is a potent inducer of CYP3A4, CYP2C9, and P-glycoprotein. It accelerates the breakdown of a huge range of medications — meaning it can silently make them stop working. Check every drug you take with a pharmacist before starting it.
- It has caused unintended pregnancies (by defeating oral contraceptives), biopsy-confirmed organ transplant rejection (by collapsing ciclosporin/tacrolimus levels), HIV treatment failure (indinavir AUC fell 57%), and reduced chemotherapy potency (irinotecan's active metabolite fell 42%). These are documented, not theoretical.
- Combined with SSRIs, SNRIs, triptans, tramadol, or other serotonergic drugs, it can cause serotonin syndrome — a potentially life-threatening reaction. Never self-combine it with an antidepressant.
- It works for mild-to-moderate depression but NOT severe depression. Depression that is severe, worsening, or accompanied by suicidal thoughts requires professional care, not a self-directed supplement.
- Hypericin is photosensitizing — expect easier sunburn and avoid tanning beds while taking it.
- Avoid during pregnancy and lactation. Hypericin and hyperforin are detected in breast milk, and long-term safety in pregnancy has not been established. If you are pregnant, planning pregnancy, or nursing, do not take St. John's Wort without consulting your prescriber.
- The size of St. John's Wort's drug interactions tracks its hyperforin content, not hypericin. Roughly 1 mg/day of hyperforin or more is the threshold for clinically significant CYP3A4 and P-glycoprotein induction — check a product's hyperforin (not hypericin) standardization to gauge interaction risk.
Frequently asked
Does St. John's Wort actually work for depression?
Yes, for mild-to-moderate depression. The Cochrane review of 29 trials (5,489 patients) found standardized extracts comparable to SSRIs with fewer side effects — it's one of the few herbal remedies that genuinely works for its headline claim. The catch: it does NOT work for severe depression (the large US NIH trial was null), and its drug interactions are dangerous enough that it should never be treated as a casual over-the-counter mood booster.Why is St. John's Wort so dangerous with other medications?
It powerfully switches on the body's drug-metabolizing enzymes (especially CYP3A4) and the P-glycoprotein transporter, which speeds up the breakdown of many medications and drops their blood levels. This has caused unintended pregnancies (it defeats the pill), organ transplant rejection, HIV treatment failure, reduced chemotherapy effectiveness, and loss of anticoagulant control. Always check with a pharmacist first.Can I take St. John's Wort with my antidepressant?
No — not without medical supervision. St. John's Wort raises serotonin activity, so combining it with an SSRI, SNRI, triptan, tramadol, or MAOI can cause serotonin syndrome, a potentially life-threatening reaction. If you're considering switching from a prescription antidepressant to St. John's Wort, do it with your prescriber, not on your own.Does St. John's Wort affect birth control?
Yes, and this is a serious risk. It accelerates the breakdown of contraceptive hormones, causing breakthrough bleeding and breakthrough ovulation. Unintended pregnancies have been reported in women combining it with the pill. If you take hormonal contraception, either avoid St. John's Wort or use a reliable backup method and talk to your prescriber.What form and dose should I look for?
The depression trials used standardized extracts — WS 5570 and LI 160 — typically at 600–1,200 mg/day, standardized to about 0.3% hypericin or a defined hyperforin content. Unstandardized retail products may not match the trial potency. But before taking any of it, list every medication you use and check it with a pharmacist — the interactions matter more than the dose.
References
- 01NCCIH — St. John's Wort (NIH)
- 02Linde et al., 2008 — St. John's wort for major depression (Cochrane)
- 03LiverTox / StatPearls — St. John's Wort drug interactions (NCBI Bookshelf)
- 04Examine.com — St. John's Wort
Last reviewed2026-05-24