Drug Side Effects
The organization of the ANS permits an understanding of effects that drugs can have on organs other than those that are the intended targets of drug action. For example, drugs that are designed to reduce heart rate by activating mAChRs on the heart activate mAChRs throughout the ANS unless subtypes of mAChR were identified on the heart and the drug selectively activates that subtype. The therapeutic and adverse effects of a drug are sometimes a function of intended use. The same drug (eg, an mAChR antagonist) in one clinical setting may be given to treat diarrhea and cause sensitivity to light (mydriasis) as an adverse effect; in another clinical setting, the drug may be used therapeutically for an eye examination, but it could cause constipation as an adverse effect. The drug-induced effects are the same in both cases. Also, drugs that have different therapeutic targets can share a similar side effect.