Six substituted phenethylamines (2C-C, 2C-D, 2C-E, 2C-I, 2C-T-2, and DOC) depress mouse locomotor activity, though 2C-D and 2C-E stimulate activity at low doses. Most fully substitute for hallucinogenic training compounds in rats, but none fully substitute for methamphetamine. All are full agonists at 5-HT2A and 5-HT2C receptors in inositol phosphate assays, and most are partial to full agonists in 5-HT2A arachidonic acid release assays, except 2C-I (antagonist). Only 2C-I shows moderate affinity for the serotonin transporter. The discriminative stimulus effects of most compounds resemble hallucinogens, not methamphetamine, but 2C-T-2 does not produce hallucinogen-like effects despite being a full agonist at 5-HT2A and 5-HT2C receptors.
Iboga alkaloids, including ibogaine, its metabolite noribogaine, and the synthetic compound 18-methoxycoronaridine (18-MC), were tested for their ability to activate the μ-opioid receptor (MOR), a common target of opioid drugs. In rat thalamic membranes, all three compounds acted as antagonists, blocking the receptor rather than activating it, with functional Ke values ranging from 3 μM for ibogaine to 13 μM for noribogaine and 18-MC. None of the compounds stimulated MOR-related G protein activity in cells expressing human or rat MORs, and only limited partial agonist effects were seen in mouse MOR-expressing cells. The findings indicate that an opioid agonist mechanism does not explain these alkaloids' effects on opioid withdrawal, supporting a novel mechanism of action and justifying further search for alternative targets.