4-DAMP (1,1-dimethyl-4-diphenylacetoxypiperidinium iodide) is a selective muscarinic acetylcholine receptor (mAChR) M<sub>3</sub> antagonist. It is also able to antagonize M<sub>1</sub> receptors but has preferential activity at the M<sub>3</sub> receptor. It competitively binds to the acetylcholine binding site on mAChRs, causing right-ward shift in the dose response curves for mAChR agonists.