Final answer:
Activation of opioid receptors does not lead to diarrhea; instead, it causes analgesia, reduced coughing, and may cause emesis. Opioids are used in anti-diarrhea medications because they decrease intestinal peristalsis.
Step-by-step explanation:
Stimulation of opioid receptors leads to a variety of physiological effects. Among these effects, analgesia, which is the reduction of pain without loss of consciousness, and reduced coughing are well-documented outcomes of activating these receptors. Opioids also commonly cause emesis (nausea and vomiting) as a side effect, especially at higher doses or during initial use. However, they are often used in anti-diarrhea medications due to their effect of decreased intestinal peristalsis, which actually helps to mitigate diarrhea. Therefore, the correct answer to which effect is NOT associated with opioid receptor stimulation is A) Diarrhea.