The drug methacholine can stimulate parasympathetic receptors in the airways,causing bronchoconstriction.Epinephrine can stimulate $\beta$₂ receptors in the airways,causing bronchodilation.These two opposing effects that cancel each other out are an example of

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Chemical antagonism is a direct chemical interaction between a drug and a biologic mediator,which inactivates the drug.Functional antagonism occurs when two drugs each produce an effect and the effects cancel each other out.Competitive antagonism occurs when a drug has an affinity for a receptor but no efficacy and at the same time blocks the active agonist from binding to and stimulating the receptor.Synergism occurs when two drugs act on a target organ by different mechanisms of action and the effect of the drug pair is greater than the sum of the separate effects of the drugs.

The Drug Methacholine Can Stimulate Parasympathetic Receptors in the Airways,causing β\betaβ

The Drug Methacholine Can Stimulate Parasympathetic Receptors in the Airways,causing $\beta$