In AIDS Clinical Trials Group A5095, 9% of participants who experienced an adverse event related to efavirenz substituted nevirapine. Most adverse events resolved; 15 participants ultimately discontinued nevirapine therapy. Grade 3/4 hepatotoxicity was observed in 14% of individuals who substituted nevirapine, compared with 6% who continued efavirenz therapy. Substitution of nevirapine because of efavirenz toxicity was generally safe and efficacious. Clinical trials registration. NCT00013520 .