The safety and efficacy of combination ezetimibe/simvastatin (E/S) plus extended-release niacin was assessed in 942 patients with type IIa/IIb hyperlipidemia for 64 weeks in a randomized, double-blind study. Patients received E/S (10/20 mg) plus niacin (to 2 g) or E/S (10/20 mg) for 64 weeks, or niacin (to 2 g) for 24 weeks and then E/S (10/20 mg) plus niacin (2 g) or E/S (10/20 mg) for an additional 40 weeks. The primary end point, the safety of E/S plus niacin, included prespecified adverse events (ie, liver, muscle, discontinuations due to flushing, gallbladder-related, cholecystectomy, fasting glucose changes, new-onset diabetes). The secondary end points included the percentage of change from baseline in high-density lipoprotein (HDL) cholesterol, triglycerides, non-HDL cholesterol, and low-density lipoprotein cholesterol, other lipids, lipoprotein ratios and high-sensitivity C-reactive protein. The anticipated niacin-associated flushing led to a greater rate of study discontinuations with the E/S plus niacin regimen than with E/S alone (0.7%, p <0.001). The rate of liver and muscle adverse events was low (<1%) in both groups. Four patients had gallbladder-related adverse events; 1 patient in the E/S and 1 in the E/S plus niacin group underwent cholecystectomy. The occurrence of new-onset diabetes was 3.1% for the E/S and 4.9% for the E/S plus niacin group. The fasting glucose levels increased to greater than baseline during the first 12 weeks (E/S, 3.2 mg/dl; E/S plus niacin, 7.7 mg/dl) and gradually decreased to pretreatment levels by 64 weeks in both groups. E/S plus niacin significantly improved HDL cholesterol, triglycerides, non-HDL cholesterol, low-density lipoprotein cholesterol, apolipoprotein B and A-I, and lipoprotein ratios compared with E/S (p <or=0.004). The changes in high-sensitivity C-reactive protein were comparable for both groups. In conclusion, the combination of E/S plus niacin was generally well tolerated, aside from niacin-associated flushing, and was significantly superior to E/S alone in improving several lipoprotein parameters during a 64-week trial in patients with hyperlipidemia. E/S plus niacin provided a broad, lipid-altering therapeutic option for these patients, even in the presence of diabetes with glucose monitoring.