What are the possible side effects of abacavir (Ziagen)? Stop using abacavir and call your doctor at once if you have symptoms of an allergic reaction from two or more of these specific side effect groups: Group 1 - fever; Group 2 - rash; Group 3 - nausea, vomiting, diarrhea, stomach pain; Group 4 - general ill feeling, extreme tiredness, body aches;