Tiomergine (INNTooltip International Nonproprietary Name; developmental code name CF 25-397) is a dopamine receptor agonist of the ergoline family which was never marketed.^[1][2][3][4] It is an analogue of the antiparkinsonian agent pergolide.^[1][2]

In addition to its dopamine receptor agonism, tiomergine also acts as a potent serotonin receptor agonist, including binding to serotonin 5-HT₁ and 5-HT₂ receptors, and might actually act primarily via its serotonin receptor agonism.^[5][6][7][8] The drug produces antiparkinsonian-like effects in rodents.^[9] In contrast to other dopamine receptor agonists however, it produces little to no stereotypy.^[9] In addition, tiomergine produces little change in locomotor activity on its own but reverses reserpine-induced catalepsy.^[9] Unlike many other dopamine receptor agonists like pergolide, tiomergine has been identified as a selective or preferential dopamine autoreceptor agonist, with little activity at postsynaptic receptors.^[10][11][12]

In contrast to animal studies, tiomergine caused severe deterioration in parkinsonism symptoms in humans in a clinical trial.^[13][14] It was also ineffective in treating psychosis in people with schizophrenia.^[15] Besides these uses, tiomergine has been investigated for the treatment of dyskinesia and dystonia.^[16][17] However, it was ineffective for tardive dyskinesia as well.^[17]

Tiomergine was first described in the scientific literature by 1976.^[9] It was developed by Sandoz.^[3]

• Substituted ergoline