 Activation of 5-HT2A receptors can induce hallucinations, and the activation of 5-HT2B receptors has been implicated in cardiac valvular insufficiency and possibly in pulmonary hypertension.In the late 1960s, non-selective serotonin receptor antagonists demonstrated a relationship between serotonin receptors and food intake.Later, animal studies showed that serotonin receptor agonists might act as a mediator of satiety.