Clindamycin side effects last how long ?

Varies among people: With Clindamycin or any antibiotic, one can get tummy upset, looser stools, even watery diarrhea. Usually the symptoms go away when the antibiotics are stopped, but if one gets an overgrowth of clostridium difficile bacteria, he can end up with diarrhea until a special antibiotic is used. Allergic rashes can last a few days, but can be much longer in a few unlucky people. A doctor can evaluate.

Not too long: Depends on how long you were taking clindamycin. Most common side effects with this antibiotic are diarrhea, possibly cramps, etc. In general, should not last more than a few days. Controversial data on using probiotics to replace GI bacteria at this time.

Sometimes a while: Clindamycin was the first antimicrobial to be linked to pseudo membranous enterocolitis, a potential serious and even life threatening infection due to clostridium difficile. If diarrhea continues especially with a kind of mousy/musty odor, seek medical attention.