St. John's Wort is a flowering plant sold as a standardized oral extract for low mood. It eases mild-to-moderate low mood about as well as standard antidepressant medications, with fewer side effects; menopausal, premenstrual, and seasonal signals are weaker. The defining issue is interference, not toxicity: it speeds drug clearance, quietly weakening birth control, blood thinners, and transplant medicines. (Full Review)
| Marker | Target | Why |
|---|---|---|
| PHQ-9 (depression symptom score) | 0–4 (minimal) | Tracks whether mood is actually improving |
| ALT (liver enzyme) | < 25 U/L (men), < 20 U/L (women) | Screens for the rare liver signal and baseline for interacting drugs |
| INR (blood-clotting time) | Condition-specific (typically 2.0–3.0 if on warfarin) | Detects loss of blood-thinning effect from enzyme induction |
| hs-CRP (inflammation marker) | < 1.0 mg/L | Tracks the inflammation–mood link and a longevity-relevant marker |
| TSH (thyroid function marker) | 1.0–2.0 mIU/L | Rules out thyroid disease masquerading as depression |
| 25-hydroxyvitamin D | 40–60 ng/mL | Low vitamin D is linked to low mood and is easily corrected |
Cadence: Baseline; reassess mood and tolerability at about 2 and 6 weeks, then every 3–6 months during continued use. On an interacting essential medication, add drug-specific checks (INR within 1–2 weeks of starting and stopping).