Is hypericin responsible for the antidepressant effect of St. John's Wort?

Only in part. Hypericin was once regarded as the main active constituent, but current evidence points to hyperforin as playing the larger role in the mood-supporting effect. Hypericin weakly inhibits MAO and mildly modulates serotonin, but its dominant property is its light-activated photodynamic action.

Why can hypericin cause sun sensitivity?

Hypericin is a photosensitizer: on absorbing light it enters an excited state and transfers energy to oxygen, generating reactive oxygen species. In the skin and eyes this can cause a phototoxic reaction, exaggerated sunburn or light sensitivity, especially at higher intakes.

Can you buy pure hypericin?

Essentially not as a standalone product. Hypericin is the standardized marker compound of St. John's Wort extracts, and most human data concern the whole extract rather than the isolated pigment.

Clinical ResearchResearch compoundLimited evidence

Hypericin

Name: Hypericin
Creator: MolekulaX

The red pigment of St. John's Wort, a weak MAO inhibitor and strong light-activated photosensitizer.

HerbMood SupportMood SupportHerbSerotoninnoo.affects.moodnoo.affects.inflammation

Pharmacology

ClassMood Support · Herb

Primary targetWeak monoamine oxidase inhibition

Targets4 receptor targets

Half-lifeLong, on the order of a day or more

OnsetAs part of a standardized extract, taken with meals; antidepressant effect develops over weeks

EvidenceLimited evidence

Affected systemsSerotoninnoo.affects.moodnoo.affects.inflammation

Contents

WHAT IS HYPERICIN?

Detailed overview

Hypericin is a naphthodianthrone red pigment and one of the marker constituents of St. John's Wort (Hypericum perforatum), long associated with the plant's mood-supporting reputation. In preclinical studies it weakly inhibits monoamine oxidase and modestly influences serotonergic signaling, though the antidepressant effect of St. John's Wort is now attributed more to hyperforin than to hypericin. Its most pronounced pharmacological property is photodynamic: when it absorbs visible or ultraviolet light it is raised to an excited state and transfers that energy to surrounding oxygen, generating singlet oxygen and other reactive oxygen species, which underlies both its phototoxicity and its activity against enveloped viruses. Evidence for the isolated pigment is limited and mostly preclinical; human data almost always concern the standardized whole extract.

Mechanism

Weak MAO inhibition + light-activated ROS generation

Evidence

Limited (mostly preclinical)

Source

Pigment of St. John's Wort (Hypericum perforatum)

Receptor profile

Reactive oxygen species (light-activated)Strong
Enveloped virusesModerate
Monoamine oxidaseWeak
Serotonergic signalingWeak

Safety

Side effects, stop signs, contraindications

Side effects · 5

Photosensitivity (phototoxicity): exaggerated sunburn and skin reactions in sunlight at higher intakes
Skin rash, tingling or stinging on sun-exposed skin
Eye sensitivity to bright light
Mild stomach upset, nausea
As part of St. John's Wort (Hypericum perforatum) extract, numerous drug interactions

Contraindications · 4

Pregnancy and breastfeeding: safety not established, avoid
Intense sun exposure or tanning beds: avoid at high doses due to phototoxic effect
SSRIs, MAO inhibitors or other serotonergic agents: theoretical risk of serotonin syndrome
As St. John's Wort extract, a strong CYP3A4 and P-glycoprotein inducer: may reduce the effect of contraceptives, anticoagulants, immunosuppressants and HIV drugs

Related Nootropics

Same therapeutic category

Studies

Related research and clinical findings

J Ethnopharmacol. 2015

LC-MS/MS based studies on the anti-depressant effect of hypericin in the chronic unpredictable mild stress rat model

Zhai XJ, et al.

PMID: 25957811Open

Brain Res. 2002

Long-term effects of St. John's wort and hypericin on monoamine levels in rat hypothalamus and hippocampus

Butterweck V, et al.

PMID: 11879791Open

Pharmacopsychiatry. 2001

In vitro binding studies with two hypericum perforatum extracts--hyperforin, hypericin and biapigenin--on 5-HT6, 5-HT7, GABA(A)/benzodiazepine, sigma, NPY-Y1/Y2 receptors and dopamine transporters

Gobbi M, et al.

PMID: 11518075Open

J Geriatr Psychiatry Neurol. 1994

Inhibition of MAO and COMT by hypericum extracts and hypericin

Thiede HM, Walper A

PMID: 7857510Open

Planta Med. 1984

Inhibition of monoamine oxidase by hypericin

Suzuki O, et al.

PMID: 6484033Open

FAQ

The red pigment of St. John's Wort, a weak MAO inhibitor and strong light-activated photosensitizer.

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Structure & chemistry

TypeHerb

FormulaC30H16O8

UpdatedJuly 10, 2026

MolekulaX Editorial Team·Source-verified · PubMed · FDA · EMA

Updated: July 10, 2026

The information here is strictly for educational and scientific purposes. It does not replace medical advice or clinical consultation, and it does not encourage illegal substance or pharmaceutical use. Data is sourced. When in doubt, consult your doctor.