Which of the following is a gastrointestinal side effect of SSRIs?

The correct response highlights that SSRIs (selective serotonin reuptake inhibitors) can lead to a range of gastrointestinal side effects, which include constipation, nausea, and diarrhea.

SSRIs influence the balance of serotonin in the brain, but they also affect serotonin levels in the gastrointestinal tract, where a large amount of the body's serotonin is found. This is significant because serotonin plays a role in regulating bowel movements and the function of the gastrointestinal tract.

Therefore, patients may experience nausea as the medication can stimulate the vagus nerve, which can lead to nausea and stomach discomfort. Additionally, the alteration in gastrointestinal motility can result in diarrhea or constipation. The variability in symptoms among individuals is notable, as some may experience one or more of these side effects concurrently.

In summary, the answer encompasses the fact that SSRIs can cause multiple gastrointestinal issues, making "All of the above" the most comprehensive and accurate choice.