What Can Be Done With My Friends Stomach Issues ?

What can be done with my friends stomach issues ? He hasnt really been able to expel anything except for watery diarrhea lately and am getting worried. He was on a cruise to Cozumel last week and not sure if there was something he may have ingested ( parasite, etc). Also he smoked some meth ( from what I understand) last week after the trip and thought it could be that too. However, he has never experienced this before while smoking. Please help, thx !!