"meta"-Chlorophenylpiperazine (mCPP) is a 5-HT2C-preferring serotonin receptor agonist that induces anxiety and depression and can cause panic attacks in susceptible individuals.2-Methyl-5-hydroxytryptamine (2-methylserotonin) and quipazine are moderately selective agonists of the 5-HT3 receptor that are used in scientific research.