Name a common side effect of opioid medications.

Opioid medications are known for several side effects due to their effect on the body's nervous system. One widely recognized side effect is constipation. Opioids work by binding to specific receptors in the brain and gastrointestinal tract, which can slow down gastrointestinal motility. This slowing of movement leads to an increased time for water absorption from the stool, resulting in harder, less frequent bowel movements, and ultimately, constipation.

The other options, while they may occur with opioid use, are not as commonly associated with opioids as constipation is. Nausea can happen, but it is often manageable and not as universal among all patients taking opioids. Insomnia can occur, but this is less frequently reported compared to constipation. Weight gain isn't typically a direct side effect associated with opioids, and in many cases, individuals may experience weight loss due to nausea and changes in appetite. Therefore, constipation stands out as a hallmark side effect of opioid therapies.