THC (Cannabis) & Thyroid Function Tests: Current Evidence

Research on Δ⁹‑tetrahydrocannabinol (THC) effects on thyroid function tests (TFTs) is limited and inconsistent.

Reported Findings

• TSH: Some cross‑sectional studies show lower TSH in heavy users; others no difference. Direction unclear.
• Free T4 / Free T3: Mostly unchanged; occasional mild elevations or reductions not clinically significant.
• Thyroid antibodies (TPOAb, TgAb): No consistent association.

Potential Mechanisms

• Endocannabinoid receptors (CB1, CB2) present in thyroid; may modulate hormone synthesis/secretion.
• THC inhibits TSH release from pituitary in animal models.
• Hepatic enzyme induction (CYP450) → altered levothyroxine metabolism.

Clinical Implications

• No guideline recommends routine TFT adjustment for cannabis use.
• Patients on levothyroxine: Monitor TSH 6–8 weeks after starting/stopping heavy cannabis; dose adjust if needed.
• Acute THC intoxication can cause transient tachycardia, hypotension – may mimic thyroid storm but TFTs normal.

Research Gaps

• Longitudinal studies with controlled dosing.
• CBD‑specific effects (may differ from THC).
• Impact on thyroid autoimmunity progression.

Advice: Disclose cannabis use to endocrinologist; don't self‑adjust thyroid medication.