St. Johns Wort

St. John’s wort (Hypericum perforatum) contains active constituents (notably hyperforin and hypericin) that appear to increase levels of neurotransmitters involved in mood regulation (serotonin, norepinephrine, dopamine), modulate GABA/glutamate systems, and affect enzyme systems — changes similar in direction to conventional antidepressants. Because SAD is a seasonal form of depressive illness, herb-driven antidepressant effects can reduce depressive symptoms in some people with SAD. Multiple reviews call the antidepressant effect “multifactorial” rather than a single, fully-understood mechanism. EBM Consult

Key mechanistic points (with evidence):

• Neurotransmitter reuptake inhibition: Extracts inhibit reuptake of serotonin, norepinephrine and dopamine in vitro/animal models — a plausible antidepressant mechanism. EBM Consult
• Hyperforin-driven PXR/CYP effects: Hyperforin is also the component that induces liver enzymes (CYPs) and P-gp transporter — this explains important drug interactions (see warnings). EBM Consult
• Additional receptor/modulatory effects: There is evidence for GABA/glutamate receptor modulation and other intracellular effects that could add to mood benefit. EBM Consult

Why that matters for SAD: SAD is a seasonal subtype of depressive disorder. Treatments that reduce depressive symptoms (light therapy, CBT, antidepressants) are effective in SAD; because St. John’s wort has demonstrated antidepressant activity in mild–moderate depression, it has been evaluated for SAD and produced positive findings in small studies (see clinical-evidence section). Reviews consider the evidence for SAD tentative but limited because trials are small. NCCIH

Typical dosing used in clinical trials (adult):

• Most commonly studied: 900 mg/day total, often given as 300 mg three times daily of a standardized extract (e.g., 0.3% hypericin formulations) — this is the regimen most often reported in trials for depression and appears in many clinical summaries. Some SAD trials also used 900 mg/day. WebMD

Form & standardization:

• Use standardized extracts (look for stated hypericin or hyperforin content). Different products vary a lot — efficacy and interaction risk depend on composition (especially hyperforin content). Clinical trial extracts are standardized; over-the-counter products are variable. WebMD

How to start and monitor:

• Talk with your clinician first. Because of major drug interactions and safety issues (below), a prescriber/pharmacist should review your medicines before starting. NCCIH
• Duration: Most trials tested up to 6–12 weeks for acute effect. Some safety data exist for longer use, but evidence on long-term SAD prevention is limited. If you plan seasonal/prolonged use (multiple months), do this under clinical supervision. Cochrane
• If switching from an SSRI or other antidepressant: allow a washout period (commonly cited ~2 weeks) before starting St. John’s wort and likewise wait before starting an SSRI after stopping SJW — to reduce risk of serotonin syndrome and other adverse effects. (Exact timing depends on the drugs involved; clinician should advise.) WebMD
• If using alongside light therapy or CBT: trials evaluated SJW alone and in combination with light therapy; combining therapies is common in clinical practice but you should check with your clinician because combined serotonergic treatments raise interaction/side-effect concerns. Evidence for additive benefit with light therapy in SAD is not strong and trials are small. NCCIH

Quality & product selection tips:

• Choose products with third-party testing (e.g., USP, NSF) or reputable brands that list hypericin/hyperforin content. Because supplements are not regulated as rigorously as prescription drugs, product quality matters. NCCIH

Broad systematic evidence (mild–moderate depression)

• Cochrane evidence & systematic reviews: Multiple systematic reviews and meta-analyses find SJW extracts are more effective than placebo for mild–moderate depression and in many trials show similar efficacy to standard antidepressants with fewer side effects in short trials. (These are key sources about the overall antidepressant effect on which SAD use is based.) Cochrane

SAD-specific trials / reviews: (important — evidence is small)

• Kasper (1997) / Pharmacopsychiatry: A trial reporting symptom reduction in SAD using 900 mg H. perforatum (short trial). (Described in reviews and in Springer chapter summaries.) SpringerLink
• Older SAD trials (1990s): Small controlled trials (for example one 1994 small trial and a larger 1999 trial comparing SJW and light therapy combinations) showed improvements in both SJW and comparator groups but were underpowered for firm conclusions about superiority. Reviews note these trials but judge the evidence limited because of small sample sizes and heterogeneity. NCCIH

Recent reviews & summaries (context + safety):

• NCCIH summary & research digest: Notes SJW “may improve some symptoms of SAD” but emphasizes the evidence is limited and small. NCCIH provides a balanced summary of research and safety. NCCIH
• Clinical overviews / meta-analyses: Several modern reviews/meta-analyses confirm efficacy in mild–moderate depression and describe SAD evidence as tentative. For example, systematic reviews and pharmacology reviews summarize the SAD trials and general clinical evidence. ScienceDirect