Methiothepin mesylate is a 5-HT receptor antagonist, with pK d s of 7.10, 7.28, 7.56, and 6.99 for 5-HT 1A , 5HT 1B , 5HT 1C , 5HT 1D . Methiothepin mesylate also shows pK d s of 7.0, 7.8, 8.74, and 8.99 for 5-HT 5A , 5-HT 5B , 5-HT 6 , and 5-HT 7 , respectively. Methiothepin exhibits high affinity at 5-HT 2A , 5HT 2B , and 5HT 2C with pK i s of 8.50, 8.68, and 8.35, respectively.