Common name: Klamath weed
Botanical name: Hypericum perforatum
© Steven Foster
Parts used and where grown
St. John’s wort is found in Europe and the United States. It is especially abundant
in northern California and southern Oregon. The above-ground (aerial) parts of the plant are
gathered during the flowering season.
St. John’s wort has
been used in connection with the following conditions (refer to the
individual health concern for complete information):
Historical or traditional use (may
or may not be supported by scientific studies)
In ancient Greece, St. John’s wort was used to treat many ailments, including
sciatica and poisonous reptile bites. In Europe, St. John’s wort was used by herbalists
for the topical treatment of wounds and burns. It is also a folk remedy for kidney and
lung ailments as well as for depression.
The major constituents in St. John’s wort include hypericin and other dianthrones, flavonoids, xanthones, and
hyperforin.1 While it was previously thought the antidepressant actions of St.
John’s wort were due to hypericin and the inhibition of the enzyme monoamine
oxidase,2 current research has challenged this belief, focusing on other
constituents, such as hyperforin, and flavonoids.3 4 5 Test
tube studies suggest that St. John’s wort extracts may exert their antidepressant
actions by inhibiting the reuptake of the neurotransmitters serotonin, norepinephrine, and
dopamine.6 This action is possibly due to the constituent hyperforin.7
St. John’s wort is able to act as an antidepressant, by making more of these
neurotransmitters available to the brain.
How much is usually taken?
The standard recommendation for mild to moderate depression is 500–1,050 mg of St.
John’s wort extract per day.8 9 10 Results may be noted
as early as two weeks. Length of use should be discussed with a healthcare professional. For
more severe depression, higher intakes may be used, under the supervision of a healthcare
Are there any side effects or interactions?
St. John’s wort has a low incidence of side effects compared to prescription
antidepressants. An adverse events profile of St. John’s wort found that, of 14
controlled clinical trials, seven reported no adverse reactions, two had no information, and
five reported a total of seven mild reactions.11 Adverse effects reported included
stomach upset, fatigue, itching, sleep disturbance, and skin rash. The rate of adverse
reactions was always similar to that of the placebo. Additionally, in seven trials comparing
St. John’s wort with other antidepressants, the adverse reaction rate for St.
John’s wort was consistently lower than that of the antidepressant drugs with which it
St. John’s wort can make the skin more sensitive to sunlight.12 Therefore,
fair-skinned people should be alert for any rashes or burns following exposure to the sun.
Three cases of severe blistering and burns were reported in people taking St. John’s
wort internally or applying it topically and then being exposed to sunlight.13
There is a case report of a woman experiencing neuropathy (nerve injury and pain) in
sun-exposed skin areas after taking 500 mg of whole St. John’s wort for four
weeks.14 Although St. John’s wort has photosensitizing properties, the
severity of this reaction is not typical for people taking the herb.
People with a history of manic-depressive illness (bipolar disorder) or a less severe condition known as
hypomania, should avoid use of St. John’s wort as it may trigger a manic
episode.15 16 17 18
There is a single case report in which ingestion of St. John's wort appeared to cause high blood pressure in a 56-year-old man. The
blood pressure returned to normal when the herb was discontinued.19
Are there any drug
Certain medicines may interact with St. John’s wort. Refer to drug interactions for a list of those medicines.
Caution: It is likely that there are many drug interactions with St.
John's wort that have not yet been identified. St. John's wort stimulates a drug-metabolizing
enzyme (cytochrome P450 3A4) that metabolizes at least 50% of the drugs on the
market.20 Consequently, St. John's wort could potentially interfere with a large
number of medications. Individuals taking any medication should, therefore, consult with a
physician before taking St. John's wort.
1. Gruenwald J. Standardized St. John’s wort clinical monograph.
Quart Rev Nat Med 1997;Winter:289–99.
2. Suzuki O, Katsumata Y, Oya M. Inhibition of monoamine oxidase by
hypericin. Planta Med 1984;50:272–4.
3. Holzl J, Demisch L, Gollnik B. Investigations about antidepressive and
mood changing effects of Hypericum perforatum. Planta Med 1989;55:643.
4. Chatterjee SS, Koch E, Noldner M, et al. Hyperforin with hypericum
extract: Interactions with some neurotransmitter systems. Quart Rev Nat Med
5. Calapai G, Crupi A, Firenzuoli F, et al. Effects of Hypericum
perforatum on levels of 5-hydroxytryptamine, noradrenaline and dopamine in the cortex,
diencephalon and brainstem of the rat. J Pharm Pharmacol 1999;51:723–8.
6. Müller WE, Rolli M, Schäfer C, Hafner U. Effects of
hypericum extract (LI 160) in biochemical models of antidepressant activity.
7. Müller WE, Singer A, Wonnemann M, et al. Hyperforin represents
the neurotransmitter reuptake inhibiting constituent of hypericum extract.
8. Brown DJ. Herbal Prescriptions for Better Health. Rocklin,
CA: Prima Publishing, 1996, 159–65.
9. Woelk H. Comparison of St. John’s wort and imipramine for
treating depression: Randomized controlled trial. BMJ 2000;321:536–9.
10. Philipp M, Kohnen R, Hiller KO. Hypericum extract versus imipramine
or placebo in patients with moderate depression: randomized multicenter study of treatment for
eight weeks. BMJ 1999;319:1534–9.
11. Ernst E, Rand JI, Barnes J, et al. Adverse effects profile of the
herbal antidepressant St. John’s wort (Hypericum perforatum L.) Eur J Clin
12. Brockmöller J, Reum T, Bauer S, et al. Hypericin and
pseudohypericin: Pharmacokinetics and effects on photosensitivity in humans.
13. Lane-Brown MM. Photosensitivity associated with herbal preparations
of St. John’s wort (Hypericum perforatum). MJA 2000;172:302[Letter].
14. Bove GM. Acute neuropathy after exposure to sun in a patient treated
with St John’s Wort. Lancet 1998;352:1121–2 [letter].
15. Nierenberg AA, Burt T, Matthews J, Weiss AP. Mania associated with
St. John’s wort. Biol Psychiatry 1999;46:1707–8.
16. Moses EL, Mallinger AG. St. John’s wort: Three cases of
possible mania induction. J Clin Psychopharmacol 2000;20:115–7.
17. O’Breasail AM, Argouarch S. Hypomania and St John’s wort.
Can J Psychiatry 1998;43:746–7 [letter].
18. Schneck C. St. John’s wort and hypomania. J Clin
Psychiatry 1998;59:689 [letter].
19. Zullino D, Borgeat F. Hypertension induced by St. John's Wort: a case
report. Pharmacopsychiatry. 2003;36:32.
20. Markowitz JS, Donovan JL, DeVane CL, et al. Effect of St John's wort
on drug metabolism by induction of cytochrome P450 3A4 enzyme. JAMA