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St. John's wort taken alone usually does not cause immediate side effects. In a study designed to look for side effects, 3,250 people took St. John's wort for 4 weeks. 1 Overall, about 2.4% reported problems. The most common complaints were mild stomach discomfort (0.6%), allergic reactions—primarily rash—(0.5%), tiredness (0.4%), and restlessness (0.3%). Another study followed 313 individuals treated with St. John's wort for 1 year. 2 The results showed a similarly low incidence of adverse effects.
In the extensive German experience with St. John's wort as a treatment for depression, there have been no published reports of serious adverse consequences from taking the herb alone. 3 Animal studies involving enormous doses of St. John's wort extracts for 26 weeks have not shown any serious effects. 4 However, there are a number of potential safety risks with St. John's wort that should be considered. These are outlined in the following sections.
Cows and sheep grazing on St. John's wort have sometimes developed severe and even fatal sensitivity to the sun. In one study, highly sun-sensitive people were given twice the normal dose of the herb. 5 The results showed a mild but measurable increase in reaction to ultraviolet radiation. Another trial found that a one-time dose of St. John’s wort containing 2 or 6 times the normal daily dose did not cause an increased tendency to burn, nor did 7 days of treatment at the normal dose. 6 However, there is a case report of severe and unexpected burning in an individual who used St. John's wort and then received ultraviolet therapy for psoriasis. 7 In addition, two individuals using topical St. John's wort experienced severe reactions to sun exposure. 8 The morals of the story are as follows: if you are especially sensitive to the sun, don't exceed the recommended dose of St. John's wort, and continue to take your usual precautions against burning. If you are receiving UV treatment, do not use St. John’s wort at all; and if you apply St. John’s wort to your skin, keep that part of your body away from the sun.
In addition, you might get into problems if you combine St. John's wort with other medications that cause increased sun sensitivity, such as sulfa drugs and the anti-inflammatory medication piroxicam (Feldene). The medications omeprazole (Prilosec) and lansoprazole (Prevacid) may also increase the tendency of St. John's wort to cause photosensitivity. 9 Finally, a report suggests that regular use of St. John's wort might also increase the risk of sun-induced cataracts. 10 While this is preliminary information, it may make sense to wear sunglasses when outdoors if you are taking this herb on a long-term basis.
Herbal experts have warned for some time that combining St. John's wort with drugs in the Prozac family (SSRIs) might raise serotonin too much and cause a number of serious problems. Recently, case reports of such events have begun to trickle in. 11 12 This is a potentially serious risk. Do not combine St. John's wort with prescription antidepressants except on the specific advice of a physician. Since some antidepressants, such as Prozac, linger in the blood for quite some time, you also need to exercise caution when switching from a drug to St. John's wort.
Antimigraine drugs in the triptan family (such as sumatriptan, or Imitrex) and the pain-killing drug tramadol also raise serotonin levels and might interact similarly with St. John's wort. 13 However, perhaps the biggest concern with St. John's wort is that it appears to decrease the effectiveness of numerous medications, including protease inhibitors and reverse transcriptase inhibitors (for HIV infection), cyclosporine and tacrolimus (for organ transplants), digoxin (for heart disease), statin drugs (used for high cholesterol), warfarin (Coumadin) (a blood thinner), chemotherapy drugs, oral contraceptives , tricyclic antidepressants , protein pump inhibitors (like Prilosec), atypical antipsychotics like olanzapine or clozapine (for schizophrenia), anesthetics, and the new heart disease drug ivabradine. 14 In fact, there are theoretical reasons to believe that this herb might reduce the effectiveness or otherwise interact with about 50% of all medications. 15 Furthermore, suppose you are taking St. John's wort while your physician is adjusting the dosage of one of your medications to obtain an optimum balance of efficacy and side effects. A problem may then occur if you subsequently stoptaking the herb: blood levels of the drug may then rise, with potentially dangerous consequences.
Note that these proposed interactions are not purely academic: they could lead to catastrophic consequences. Indeed, St. John's wort appears to have caused several cases of heart, kidney, and liver transplant rejection by interfering with the action of cyclosporine.
The herb also appears to decrease the effectiveness of oral contraceptives 16 and by doing so is thought to have caused unwanted pregnancies. 17 On a less dramatic level, one study showed that among people taking a cholesterol-lowering medication in the statin family, use of St. John’s wort caused cholesterol levels to rise. 18 (The same would be expected to occur if you are using red yeast rice to treat high cholesterol, as red yeast rice supplies naturally-occurring statin drugs.)
Finally, some people with HIV take St. John's wort in the false belief that the herb will fight AIDS. The unintended result may be to reduce the potency of standard anti-HIV drugs.
There is some evidence that low-hyperforin St. John's wort may have less potential for drug interactions than other forms of St. John's wort. 19 Nonetheless, we recommend that people taking any oral or injected medication that is critical to their health or wellbeing should entirely avoid using any form of St. John's wort until more is known; if you are already taking the herb, you should not stop taking it until you can simultaneously have your drug levels monitored. On general principles, we also advise avoid using the herb prior to undergoing general anesthesia.
Safety in Special Circumstances
One animal study found no ill effects on the offspring of pregnant mice. 20 However, these findings alone are not sufficient to establish St. John's wort as safe for use during pregnancy. Furthermore, the St. John's wort constituent hypericin can accumulate in the nucleus of cells and directly bind to DNA. 21 For this reason, pregnant or nursing women should avoid St. John's wort. Furthermore, safety for use by young children or people with severe liver or kidney disease has not been established.
Like other antidepressants, case reports suggest that St. John's wort can cause episodes of mania in individuals with bipolar disorder (manic-depressive disease). 22 There is also one report of St. John's wort causing temporary psychosis in a person with Alzheimer's disease . 23
Certain foods contain a substance named tyramine. These foods include aged cheeses, aged or cured meat, sauerkraut, soy sauce, other soy condiments, beer (especially beer on tap). and wine. Drugs in the MAO inhibitor family interact adversely with tyramine, causing severe side effects such as high blood pressure, rapid heart rate, and delirium. One case report suggests that St. John’s might present this risk as well. 24 However, other studies suggest that normal doses of St. John’s should not cause MAO-like effects. 25 Until this issue is sorted out, we recommend that individuals taking St. John’s wort avoid tyramine-containing foods. Since MAO inhibitors react adversely with stimulant drugs such as Ritalin, ephedrine (found in the herb ephedra ), and caffeine, we also recommend that you avoid combining St. John’s wort with them.
One small study suggests that high doses of St. John's wort might slightly impair mental function. 26 One case report associates use of St. John's wort with hair loss. 27 The authors note that standard antidepressants may also cause hair loss at times.
One study raised questions about possible antifertility effects of St. John's wort. When high concentrations of St. John's wort were placed in a test tube with hamster sperm and ova, the sperm were damaged and less able to penetrate the ova. 28 However, since it is unlikely that this much St. John's wort can actually come in contact with sperm and ova when they are in the body rather than in a test tube, these results may not be meaningful in real life.
In one reported case, St. John’s Wort may have interacted with the menopause drug tibolone to produce severe liver damage. 29
Interactions You Should Know About
If you are taking:
- Antidepressant drugs, including MAO inhibitors , SSRIs , and tricyclics , or possibly the drugs tramadol or sumatriptan (Imitrex): Do not take St. John's wort at the same time. Actually, you need to let the medication flush out of your system for a while (perhaps weeks, depending on the drug) before you start the herb.
- Digoxin , cyclosporine and tacrolimus, protease inhibitors or reverse transcriptase inhibitors , oral contraceptives , tricyclic antidepressants , warfarin (Coumadin) , statin drugs , theophylline , chemotherapy drugs, newer antipsychotic medications (such as olanzapine and clozapine ), anesthetics, or, indeed, any critical medication: St. John's wort might cause the drug to be less effective. Furthermore, if you are already taking St. John's wort and your physician adjusts your medication dosage to achieve proper blood levels, suddenly stopping St. John's wort could cause the level of the drug in your body to rebound to dangerously high levels.
- Medications that cause sun sensitivity such as sulfa drugs and the anti-inflammatory medication piroxicam (Feldene) , as well as omeprazole (Prilosec) or lansoprazole (Prevacid) : Keep in mind that St. John's wort might have an additive effect.
- Stimulant drugs or herbs such as Ritalin, caffeine, or ephedrine ( ephedra ): It is possible that St. John’s wort might interact adversely with them.
- Woelk H, Burkard G, Grunwald J. Benefits and risks of the hypericum extract LI 160: Drug monitoring study with 3,250 patients. J Geriatr Psychiatr Neurol. 1994;7(suppl 1):S34-S38.
- Hubner WD, Arnoldt KH. St John's Wort: a one year treatment study [in German; English abstract]. Z Phytother. 2000;21:306-310.
- De Smet PA, Nolen WA. St. John's wort as an anti-depressant. BMJ. 1996;3:241-242.
- Schulz V, Hansel R, Tyler VE. Rational Phytotherapy: A Physicians' Guide to Herbal Medicine. 3rd ed. Berlin, Germany: Springer-Verlag; 1998:56.
- Brockmöller J, Reum T, Bauer S, Kerb R, Hübner WD, Roots I. Hypericin and pseudohypericin: pharmacokinetics and effects on photosensitivity in humans. Pharmacopsychiatry. 30 Suppl 2():94-101.
- Schempp CM, et al. 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. Arch Dermatol. 2001;137:512-513
- Lane-Brown MM. Photosensitivity associated with herbal preparations of St John's wort (Hypericum perforatum) Med J Aust. 172(6):302.
- Lane-Brown MM. Photosensitivity associated with herbal preparations of St John's wort ( Hypericum perforatum ) [letter]. Med J Aust. 2000;172:302.
- Mirossay A, Mirossay L, Tóthová J, Miskovský P, Onderková H, Mojzis J. Potentiation of hypericin and hypocrellin-induced phototoxicity by omeprazole. Phytomedicine. 6(5):311-7.
- Roberts J. Presentation: American Society for Photobiology; 1999.
- DeMott K. St. John's wort tied to serotonin syndrome. Clinical Psychiatry News. 1998;26:28.
- Gordon JB. SSRIs and St.John's Wort: possible toxicity? Am Fam Physician. 57(5):950,953.
- Mason BJ, Blackburn KH. Possible serotonin syndrome associated with tramadol and sertraline coadministration. Ann Pharmacother. 31(2):175-7.
- Jobst KA, McIntyre M, St. George D, et al. Safety of St John's wort (Hypericum perforatum). Lancet. 2000,355:575.
- Markowitz JS, Donovan JL, DeVane CL, Taylor RM, Ruan Y, Wang JS, Chavin KD. Effect of St John's wort on drug metabolism by induction of cytochrome P450 3A4 enzyme. JAMA. 290(11):1500-4.
- Murphy PA, Kern SE, Stanczyk FZ, Westhoff CL. Interaction of St. John's Wort with oral contraceptives: effects on the pharmacokinetics of norethindrone and ethinyl estradiol, ovarian activity and breakthrough bleeding. Contraception. 71(6):402-8.
- Jobst KA, McIntyre M, St. George D, et al. Safety of St John's wort (Hypericum perforatum).Lancet. 2000;355:575.
- Andrén L, Andreasson A, Eggertsen R. Interaction between a commercially available St. John's wort product (Movina) and atorvastatin in patients with hypercholesterolemia. Eur J Clin Pharmacol. 63(10):913-6.
- Mueller SC, Majcher-Peszynska J, Uehleke B, Klammt S, Mundkowski RG, Miekisch W, Sievers H, Bauer S, Frank B, Kundt G, Drewelow B. The extent of induction of CYP3A by St. John's wort varies among products and is linked to hyperforin dose. Eur J Clin Pharmacol. 62(1):29-36.
- Rayburn WF, Gonzalez CL, Christensen HD, Stewart JD. Effect of prenatally administered hypericum (St John's wort) on growth and physical maturation of mouse offspring. Am J Obstet Gynecol. 184(2):191-5.
- Miskovsky P, Chinsky L, Wheeler GV, Turpin PY. Hypericin site specific interactions within polynucleotides used as DNA model compounds. J Biomol Struct Dyn. 13(3):547-52.
- Nierenberg AA, Burt T, Matthews J, Weiss AP. Mania associated with St. John's wort. Biol Psychiatry. 46(12):1707-8.
- Laird RD, Webb M. Psychotic episode during use of St. John's wort. J Herbal Pharmacother. 2001;1:81-87.
- Patel S, Robinson R, Burk M. Hypertensive crisis associated with St. John's Wort. Am J Med. 112(6):507-8.
- Bladt S, Wagner H. Inhibition of MAO by fractions and constituents of hypericum extract. J Geriatr Psychiatr Neurol. 1994;7(suppl 1):S57-S59.
- Ellis KA, Stough C, Vitetta L, et al. An investigation into the acute nootropic effects of Hypericum perforatum L. (St. John's Wort) in healthy human volunteers. Behav Pharmacol. 2001;12:173-182.
- Parker V, Wong AH, Boon HS, Seeman MV. Adverse reactions to St John's Wort. Can J Psychiatry. 46(1):77-9.
- Ondrizek RR, Chan PJ, Patton WC, King A. An alternative medicine study of herbal effects on the penetration of zona-free hamster oocytes and the integrity of sperm deoxyribonucleic acid. Fertil Steril. 71(3):517-22.
- Etogo-Asse F, Boemer F, Sempoux C, Geubel A. Acute hepatitis with prolonged cholestasis and disappearance of interlobular bile ducts following tibolone and Hypericum perforatum (St. John's wort). Case of drug interaction? Acta Gastroenterol Belg. 71(1):36-8.