Muscarinic M3 receptors are expressed in regions of the brain that regulate insulin homeostasis, such as the hypothalamus and dorsal vagal complex of the brainstem.

[6] These receptors are highly expressed on pancreatic beta cells and are critical regulators of glucose homoestasis by modulating insulin secretion.

Because the M3 receptor is Gq-coupled and mediates an increase in intracellular calcium, it typically causes constriction of smooth muscle, such as that observed during bronchoconstriction.

[9] The muscarinic M3 receptor regulates insulin secretion from the pancreas[7] and are an important target for understanding the mechanisms of type 2 diabetes mellitus.

Some antipsychotic drugs that are prescribed to treat schizophrenia and bipolar disorder (such as olanzapine and clozapine) have a high risk of diabetes side-effects.