What are the common side effects of PrEP? PrEP is actually quite a robust medication and it doesn’t have a huge amount of side effects. Probably the most common side effect is on initiation it can cause some abdominal side effects. This includes for some people constipation, for some people loosening of the stool, and for some people bloating. What I can say is that it doesn’t happen with everybody and when it does happen, it’s usually gone within one to two weeks. There’s a number of ways that you can help reduce this risk and that includes things like taking the medicine with food, adjusting the time that you take the medicine, and sometimes acidophilus yoghurt. Anything that helps the gut biome can help reduce the effects of this particular outcome.