It has a direct relaxant effect on the smooth muscles of the respiratory tract, part of which is due to the release of endogenous adrenaline and norepinephrine. As a purine receptor blocker, it can counteract the contractile effect of adenine and other substances on the respiratory tract. It can enhance the contraction force of the diaphragm, especially when the diaphragm is weak, and is beneficial to improving respiratory function.

It can directly stimulate adrenaline receptors, and can also indirectly stimulate adrenaline receptors by prompting adrenergic nerve endings to release norepinephrine. It has a stimulating effect on both alpha and beta receptors; it can dilate bronchi and contract local blood vessels to eliminate congestion and swelling of the nasopharyngeal mucosa, relieve nasal congestion symptoms, and has a longer duration of action; it can strengthen myocardial contractility, enhance cardiac output, and ensure sufficient venous return to the heart; it has a stronger central nervous system stimulating effect than adrenaline.

Theophylline has a direct relaxant effect on the smooth muscle of the respiratory tract, and its effect is partly due to the release of endogenous adrenaline and norepinephrine. In addition, theophylline is a purine receptor blocker, which can counteract the contraction of adenine and other substances on the respiratory tract. Theophylline can enhance the contraction of the diaphragm, especially when the diaphragm is weak, so it is beneficial to improve respiratory function. Methylephedrine hydrochloride can directly stimulate adrenaline receptors, and can also indirectly stimulate adrenaline receptors by prompting adrenergic nerve endings to release norepinephrine, and has an stimulating effect on both alpha and beta receptors. It can dilate the bronchi and contract local blood vessels to eliminate congestion and swelling of the nasopharyngeal mucosa, relieve nasal congestion symptoms, and has a longer duration of action; strengthen myocardial contractility, increase cardiac output, and make venous return to the heart sufficient; it has a stronger central nervous system excitation effect than adrenaline.