Antimuscarinic drugs serve primarily as smooth muscle relaxants in the smaller pathways of the respiratory tract, and are considered to be highly effective in neutralizing bronchoconstriction. However, they are also slower than two-receptor agonists. They can take up to one hour to exert maximum effect, but their actions can last for as low as three hours, which calls for more frequent doses. Antimuscarinic drugs see a great deal of use in the field of keeping chronic asthma under control, and they can even be used to battle life-threatening cases of asthma when combined with a two-receptor agonist by way of nebulization.

The actions of certain antimuscarinic drugs can last for much longer, up to an entire day. However, they are not suitable for relieving cases of acute bronchospasm, and thus they cannot be used to keep asthmatic tendencies in check
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Antimuscarinics come with their own series of side-effects, including the likes of constipation, blurry vision, lowered saliva production and difficulties when urinating. Muscarinic receptors are present all over the body, and the drugs target all of them indiscriminately. Therefore, although they are powerful bronchodilators, they should not be used by patients suffering from other physical complications without consulting a doctor first.