Independent/Evidence-based/Sources: NIH ODS + DRILast reviewed February 2026
caredoctorevidence-based

Monograph No. 051 / Herbals & Others

Herbals & Others

St. John's Wort: Benefits, Dosage, and Safety

St. John's wort (Hypericum perforatum) is a flowering plant taken as a supplement, most often marketed for low mood, with NIH sources noting it may be as effective as standard antidepressants for mild to moderate depression but carrying many serious drug interactions.

Reviewed and edited by Maya Ellison, Health Content Editor·Last reviewed February 2026

Short answer

St. John's wort (Hypericum perforatum) is a flowering plant taken as a supplement, most often marketed for low mood, with NIH sources noting it may be as effective as standard antidepressants for mild to moderate depression but carrying many serious drug interactions.

01

What st. john's wort is

St. John's wort is a supplement made from the flowering tops of the plant Hypericum perforatum, a yellow-flowered herb native to Europe and now found widely across the United States. It is sold as capsules, tablets, teas, liquid extracts, and topical preparations. Its commonly studied constituents include hypericin and hyperforin. As a botanical, it is not an essential nutrient and has no Dietary Reference Intake.

What it does

  • It is not an essential nutrient and has no established role in normal human physiology
  • It has been used traditionally for low mood, wound healing, and other complaints
  • Laboratory work suggests its constituents may affect chemical messengers such as serotonin in the brain, though the exact mechanism in people is not fully established
  • It induces liver and gut enzymes (including CYP3A4) and a drug transporter (P-glycoprotein), which speeds the breakdown and clearance of many medicines
02

Intake and dosing

St. John's Wort is not an essential nutrient, so no Recommended Dietary Allowance or Tolerable Upper Intake Level has been set. Doses in studies vary widely. Because supplement doses are not standardised, discuss an appropriate amount with a clinician or pharmacist.

03

Deficiency and who is at risk

Not applicable. St. John's wort is a botanical, not an essential nutrient, so there is no deficiency state and no requirement for it in the diet.

04

Who may need more

  • Not applicable as an essential nutrient; no one requires it dietarily
  • People considering it for mild to moderate low mood sometimes use it, but only after discussing with a health professional because of extensive drug interactions
  • It should be avoided by anyone taking prescription medicines without medical supervision
05

Food sources

Not a food component. St. John's wort is obtained only from the Hypericum perforatum plant taken as a supplement or herbal preparation, not from any normal dietary food source.

06

Forms and absorption

Sold as capsules, tablets, teas, tinctures, liquid extracts, and topical oils and creams. Products are highly variable in composition; many oral extracts used in research were standardized to hypericin content, but the amount of active constituents differs widely between brands, so potency and effects are not consistent across products. NIH sources do not establish a standard dose.

07

Safety, excess and interactions

For most adults who are not taking any medicines, St. John's wort appears to be safe when used by mouth for up to 12 weeks; safety of longer use is not established. It interacts with a very large number of medicines and can weaken or dangerously alter their effects, so it should not be combined with prescription drugs without medical advice. It may be unsafe during pregnancy because it may increase the risk of birth defects, and there is not enough information to know if it is safe while breastfeeding. Do not stop or replace a prescribed antidepressant with St. John's wort without talking to a clinician. Because it can cause photosensitivity, limit sun exposure while using it.

Too much

Reported adverse effects include trouble sleeping, vivid dreams, restlessness, anxiety, irritability, stomach upset, diarrhea, fatigue, dizziness, headache, dry mouth, and skin tingling. St. John's wort can make skin and eyes more sensitive to sunlight (photosensitivity), and high sun exposure while using it may lead to severe skin reactions, particularly in fair-skinned people. Combining it with serotonergic medicines can raise serotonin to potentially life-threatening levels (serotonin syndrome), with symptoms such as agitation, fast heartbeat, high blood pressure, diarrhea, and hallucinations.

Interactions to know

  • Antidepressants (SSRIs, SNRIs, tricyclics such as amitriptyline, and bupropion): combined use can raise serotonin to dangerous levels and cause serotonin syndrome
  • Birth control pills (oral contraceptives): St. John's wort can reduce their effectiveness and lead to breakthrough bleeding and unintended pregnancy
  • Cyclosporine and other transplant anti-rejection drugs: levels can drop, risking organ rejection
  • Warfarin and other anticoagulants: reduced blood-thinning effect
  • Digoxin and heart medicines such as ivabradine: reduced drug levels and effectiveness
  • Anti-HIV medicines such as indinavir and nevirapine: reduced levels that can cause treatment failure
  • Cancer chemotherapy such as irinotecan, imatinib, and docetaxel: reduced effectiveness
  • Anticonvulsants such as phenytoin and carbamazepine: altered drug levels
  • Simvastatin and some other statins: reduced levels
  • Oxycodone and some other medicines: altered effect; overall it speeds breakdown of many drugs by inducing CYP3A4 and P-glycoprotein

How status is measured

Not routinely measured. There is no blood test or laboratory marker used to assess St. John's wort status because it is not an essential nutrient. Clinicians instead review a patient's full medication list to check for interactions.

Regulated by the FDA as a dietary supplement under DSHEA, not as a drug. It is not FDA-approved to diagnose, treat, cure, or prevent any disease, and supplement products are not reviewed by the FDA for safety and effectiveness before sale.

08

What the evidence supports

We grade the strength of evidence behind each common reason people take st. john's wort, mirroring how the NIH describes it.

Moderate
May be more effective than placebo and as effective as standard antidepressants for mild to moderate depression

A Cochrane review concluded St. John's wort may be better than placebo and as effective as standard prescription antidepressants for major depression of mild to moderate severity; results were more positive in German-speaking countries than in U.S. trials.

Insufficient
Effective for severe depression or for use beyond about 12 weeks

NIH sources state effectiveness for severe depression and for use longer than 12 weeks is uncertain; some U.S. trials found it no more effective than placebo for moderate major depression.

Limited
Helpful for menopausal or hot flash symptoms

Only limited research exists and the evidence has not clearly shown it to be helpful.

Insufficient
Helpful for ADHD, somatic symptom disorder, IBS, OCD, premenstrual syndrome, or smoking cessation

NIH notes the limited evidence has not clearly shown St. John's wort to be helpful for any of these conditions.

Limited
Topical use aids wound healing or skin conditions

Historically used on skin, but current evidence is limited and not conclusive.

▣

Sources

Every figure on this page is quoted from the sources above. Science changes; we re-check and re-date pages as authorities update their guidance.