THC (Δ⁹-tetrahydrocannabinol)

Δ⁹-Tetrahydrocannabinol (THC) is the cannabinoid primarily responsible for the psychoactive effects of cannabis. It binds preferentially to CB1 receptors in the central nervous system, which mediates both the therapeutic effects (analgesia, antiemesis, appetite stimulation, muscle-spasticity reduction) and the unwanted effects (cognitive impairment, anxiety at higher doses, tachycardia).

In medical use, THC-dominant formulations are considered for specific indications — notably MS spasticity, cancer-related nausea and pain, refractory chronic pain, and some neuropathic-pain syndromes — typically when first-line therapy has been inadequate. Doses are titrated conservatively from a low starting point (often 2.5 mg) because individual response varies substantially with endocannabinoid-system tone.

THC affects several CYP450 enzymes (particularly CYP3A4 and CYP2C9), which matters for patients taking warfarin, some antipsychotics, certain antiretrovirals, or hormonal contraceptives — interaction review is part of every prescribing decision. In South Africa, THC-containing medicines sit on Schedule 6 and are accessed via Section 21 authorisation. THC-dominant prescribing is generally avoided in patients with personal or strong family history of psychotic illness, in active psychosis, in pregnancy, and in adolescents whose brain development is ongoing.