Pirenzepine

Pirenzepine (Gastrozepin), an M₁ selective antagonist, is used in the treatment of peptic ulcers, as it reduces gastric acid secretion and reduces muscle spasm. It is in a class of drugs known as muscarinic receptor antagonists - acetylcholine being the neurotransmitter of the parasympathetic nervous system which initiates the rest-and-digest state (as opposed to fight-or-flight), resulting in an increase in gastric motility and digestion; whereas pirenzepine would inhibit these actions and cause decreased gastric motility leading to delayed gastric emptying and constipation. It has no effects on the brain and spinal cord as it cannot diffuse through the blood–brain barrier.

Pirenzepine has been investigated for use in myopia control.

It promotes the homodimerization or oligomerisation of M₁ receptors.