24.5 : 催吐剂和止吐剂：大麻素

Vomiting, a protective reflex to expel toxins from the gut, can become a distressing side effect of regular chemotherapy.

Neurons near the chemoreceptor trigger zone and emetic center contain cannabinoid or CB₁ receptors. When activated by tetrahydrocannabinol or THC, these receptors inhibit the release of neurotransmitters such as serotonin, halting the neurotransmission of vomiting stimuli. This makes the CB₁ receptor an attractive drug target.

Several agonist drugs like dronabinol or nabilone enhance CB₁ receptor activity, mitigating vomiting reflex.

Both agonists are given orally and act rapidly within an hour of ingestion to prevent chemotherapy-induced nausea and vomiting.

Dronabinol, a marijuana plant extract, undergoes extensive first-pass hepatic metabolism, decreasing its bioavailability. Its regimen typically involves one dose before chemotherapy and subsequent doses every 2-4 hours after.

They can cause adverse effects such as dizziness, dry mouth, euphoria, anxiety, postural hypotension, and tachycardia.