Side effects of 5-htp are similar to anything that elevates serotonin, eg SSRIs. Other than minor GI issues, I've personally experienced heartburn, erectile and libido problems (but it didn't start till my late 30s, so age is likely a factor), less appetite or feeling less hungry in general, and less emotional extremes (negative emotions are reduced which is good, but so are positive emotions). When I was growing up, I wouldn't be able to get through a few sentence without stuttering (repetitions and blocks). In stressful situations, I wouldn't be able to get any word out and if I did, I would continue repetitions for a long time. I don't remember most of it because I try to forget those really embarrassing stuttering episodes. As an adult on 5-htp, I'm fluent most of the time. It has changed over the years, but nowadays, I usually have trouble with some vowels and saying my name. Sometimes, I still have blocks and repetitions but they happen rarely.