Which medication can lead to the most gastrointestinal side effects?

The medication that is most commonly associated with gastrointestinal side effects among the options provided is actually Paroxetine, not Sertraline. While Sertraline can indeed cause gastrointestinal issues, such as nausea and diarrhea, it is often rated as having a lower incidence of these side effects compared to Paroxetine.

Paroxetine is an SSRI (selective serotonin reuptake inhibitor) that has been widely noted for causing gastrointestinal disturbances. Patients taking Paroxetine frequently report symptoms such as constipation, nausea, and diarrhea. This can occur due to its effects on the serotonin receptors in the gastrointestinal tract, which can influence motility and secretion.

Therefore, while Sertraline is also an SSRI and does have gastrointestinal side effects, Paroxetine is generally considered more likely to cause these issues, making it the medication with the highest association with gastrointestinal complaints in this particular context.