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 is 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.

[1] 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.

[2][3] It promotes the homodimerization or oligomerisation of M1 receptors.