What is the primary effect of anticholinergic drugs?

The primary effect of anticholinergic drugs is dilation of pupils, also known as mydriasis. Anticholinergics work by inhibiting the action of acetylcholine, a neurotransmitter responsible for various bodily functions, including those mediated by the parasympathetic nervous system. By blocking acetylcholine at the muscarinic receptors in the eye, these drugs lead to a relaxation of the circular muscles of the iris, resulting in pupil dilation.

In the context of the other options, constriction of pupils would be associated with cholinergic activity rather than anticholinergic effects. An increase in heart rate can occur as a secondary effect due to the blockade of vagal tone, but it is not the primary action. A decrease in respiratory rate is not a characteristic of anticholinergic medications; in fact, they may promote bronchodilation and can enhance respiratory function in certain contexts. Understanding these mechanisms is crucial for recognizing how these drugs influence various physiological responses.