In 35 double-blind trials, side effects on this herb looked much like placebo and milder than older antidepressants. The serious risks sit in 2 other places.
One is sunlight, which is smaller than its reputation. The other is the medicine cabinet, which is larger.
Quick Answer: What Are St. John's Wort's Side Effects?
Side effects are usually mild: stomach upset or diarrhea, dizziness, trouble sleeping, restlessness, headache and skin tingling. A review of 35 trials found rates similar to placebo. Sun sensitivity is real but small at usual doses. The serious risks are drug interactions and use in pregnancy, where it is not established as safe.
Key Takeaways
- 35 double-blind trials found side-effect rates close to those on placebo.
- Headache was the 1 effect clearly more common in a US trial.
- Sun sensitivity rose only slightly, even at 1800 mg daily of extract.
- Dropout for side effects ran 0 to 5.7% across 35562 observed patients.
- Drug interactions, not side effects, are the 1 serious risk here.
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The Common Side Effects
The usual list is short and mostly mild. The US government's complementary health centre gives much the same one.
- Gut: Stomach upset and diarrhea.
- Head: Dizziness and headache.
- Sleep and energy: Trouble sleeping and restlessness.
- Skin: Tingling, and reactions after sun at large doses.
NCCIH lists diarrhea, dizziness, trouble sleeping, restlessness and skin tingling, and warns of severe skin reactions after sun with large oral doses.[1]St. John's Wort: Usefulness and Safety — National Center for Complementary and Integrative Health View source What the plant is in the first place is in what this flowering herb is.
How Often, Compared With Placebo
The rates are the reassuring part of this herb's record.
| Source | What it found |
|---|---|
| 35 double-blind trials | Dropouts and side effects similar to placebo |
| Against older antidepressants | Fewer side effects |
| Against SSRIs | Slightly fewer side effects |
| 17 observational studies, 35,562 people | Dropout for side effects 0 to 5.7% |
| US trial, 2001 | Headache in 41% against 25% on placebo |
A 2004 systematic review pooled trials and large observational studies. It concluded that the most relevant adverse effects are interactions, particularly with cyclosporine.[2]Adverse effects of St. John's Wort: a systematic review — Journal of Clinical Psychiatry (2004) View source
In a US trial of 200 adults, headache was the only adverse event clearly more frequent on the herb than on placebo.[3]Effectiveness of St John's wort in major depression: a randomized controlled trial — JAMA (2001) View source
Sleep, Restlessness and the Eyes
Three questions come up often enough to answer directly.
- Sleep: Trouble sleeping is a listed side effect, so a morning dose is sensible.
- Anxiety: Restlessness is listed too, so it can feel worse at first.
- Eyes: The light studies below measured skin only, so sunglasses are a fair precaution.
- Liver: Its documented liver effect is enzyme induction.
That last point is the one that changes decisions. The same liver enzyme effect lowers many prescription drugs, which is the enzyme problem behind most of its risks.
Sun Sensitivity, Measured
Photosensitivity is on every warning list. The measurements put a size on it.
- Single doses up to 3600 mg of extract: No change to sunlight-type sensitivity.
- The top single dose: UV-A sensitivity only marginally higher.
- 15 days at 1800 mg a day: A small rise, offset by 21% less sun time.
- Typical doses: Lower than the doses tested.
That dose-finding trial used doses higher than typical products and still found little change in light sensitivity.[4]Hypericin and pseudohypericin: pharmacokinetics and effects on photosensitivity in humans — Pharmacopsychiatry (1997) View source
A later trial reported no change in skin sensitivity to UV, visible light or simulated sunlight after single or steady-state doses.[5]Single-dose and steady-state administration of Hypericum perforatum extract (St John's Wort) does not influence skin sensitivity to UV radiation, visible light, and solar-simulated radiation — Archives of Dermatology (2001) View source
Daily Use and Dose
Most side effects in the trials came from daily use over weeks, so the dose you take is part of the picture.
- Trial length: Mostly 4 to 12 weeks of daily dosing.
- Longer use: Some studies suggest a year or more is tolerated.
- Dose form: Trials used extracts, not whole herb.
- Counting sources: Blends may contain it too.
How the trial amounts compare with a herb capsule is in how much a typical daily dose contains.
Pregnancy, Breastfeeding and Mania
These are the groups for whom the side-effect list is not the main question.
- Pregnancy: Not established as safe, and a birth defect signal exists.
- Breastfeeding: Infants have shown colic, drowsiness and lethargy.
- Mania: Reported in case reports, including 1 with an SSRI.
- Bipolar disorder: Only with a psychiatrist involved.
German claims data covered 496 exposed pregnancies. Major malformations were coded in 5.8% of linked babies, a finding the authors called striking and hypothesis-generating.[6]Characterization of pregnancies exposed to St. John's wort and their outcomes: A claims data analysis — Reproductive Toxicology (2021) View source
One case report describes a manic episode in a man who kept taking the herb alongside an SSRI against medical advice.[7]Mania in a patient receiving testosterone replacement postorchidectomy taking St John's wort and sertraline — Journal of Psychopharmacology (2000) View source
Keeping the Risks Small
Four habits cover most of the practical risk.
- Check medicines first: The serious risk sits there.
- Take it early: If sleep suffers.
- Cover up: In strong sun, especially at higher doses.
- Stop and ask: For a rash, agitation or confusion.
With those habits in place, a whole-herb capsule sits at the mild end of the side-effect range, with the interaction check still coming first.
Stop and Speak to a Clinician If
- You take any prescription medicine, because this herb speeds up how the body clears many of them
- You take an antidepressant or any other medicine that acts on serotonin
- You rely on the pill or another hormonal method to prevent pregnancy
- You take warfarin, digoxin, cyclosporine, tacrolimus or any HIV medicine
- You are pregnant or breastfeeding, or have ever had a manic episode
- You have any thought of self-harm, which needs same-day help: call or text 988 in the US
Frequently Asked Questions
What are the negative effects of St. John's Wort? +
Usually mild: stomach upset, dizziness, trouble sleeping, restlessness and headache. In 35 trials rates were close to placebo.
Can you take St. John's Wort daily? +
Trials used it daily for 4 to 12 weeks. NCCIH says it appears safe for up to 12 weeks in adults taking no other medicine.
Is St. John's Wort hard on your liver? +
Liver injury is not on the NCCIH side-effect list. Its documented liver effect is switching on an enzyme that clears over 50% of drugs.
Does St. John's Wort interfere with sleep? +
It can. Trouble sleeping is 1 of the listed side effects, so a morning dose is the usual adjustment.
Can St. John's wort cause eye problems? +
The 2 light-sensitivity trials here measured skin, not eyes. Hypericin is light-sensitive, so sunglasses in strong sun are a sensible precaution.
Can St. John's Wort make anxiety worse? +
It can at first. Restlessness is 1 of its listed side effects, and it has not been shown to treat anxiety.
Does St. John's Wort make you sensitive to the sun? +
Slightly, at high doses. At 1800 mg a day of extract the effect was offset by about 21% less time in the sun.
Is St. John's Wort safe in pregnancy? +
It is not established as safe. Claims data on 496 exposed pregnancies raised a malformation signal that needs further study.
Can St. John's Wort cause mania? +
Case reports describe it, including 1 in a man also taking an SSRI. Anyone with bipolar disorder should involve a psychiatrist.
Does St. John's Wort cause headaches? +
In a US trial of 200 adults, headache affected 41% on the herb against 25% on placebo.
Related Reading
- What the Depression Research Shows
- Contraceptive Failure Risk, Explained
- Serotonin Syndrome and Antidepressants
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