BACKGROUND: The present study was designed to determine the efficacy and safety of Niaspan (Kos Pharmaceuticals, Inc, Hollywood, FL), a new controlled-release formulation of niacin, in the treatment of primary hyperlipidemia, the occurrence and severity of flushing events, and potential adverse effects, particularly hepatotoxicity. METHODS AND RESULTS: The study was conducted as a multicenter, randomized, double-blind, placebo-controlled, parallel comparison of Niaspan in doses of 1000 mg/day and 2000 mg/day, administered once a day at bedtime. One hundred twenty-two patients with low-density lipoprotein cholesterol levels >4.14 mM/L (160 mg/dL) with dietary intervention and high-density lipoprotein cholesterol =1.81 mM/L (70 mg/dL) were randomized to one of three treatment groups: placebo, and 1000 mg/day or 2000 mg/day of Niaspan. Safety and efficacy measures included 12-hour serum fasting lipid and lipoprotein concentrations, serum analyte levels for major organ function, flushing diaries, and adverse event records. The placebo group demonstrated no significant changes in serum lipoprotein concentrations over the treatment period of 12 weeks, except for a slight 4% increase in high-density lipoprotein cholesterol. Niaspan significantly lowered low-density lipoprotein cholesterol levels by 6% and 14% for the 1000 mg/day and 2000 mg/day doses, respectively. High-density lipoprotein cholesterol levels rose significantly, with a 17% increase occurring at the 1000 mg/day dose and a 23% increase occurring at the 2000 mg/day doses, respectively. High-density lipoprotein cholesterol levels rose significantly, with a 17% increase occurring at the 1000 mg/day dose and a 23% increase occurring at the 2000 mg/day dose. Niaspan (2000 mg/day) produced significant decreases of 27% and 29%, respectively, for serum lipoprotein(a) and triglyceride concentration. Although the incidence of flushing was significant, these episodes were generally well tolerated. CONCLUSION: Niaspan administered in doses of 1000 mg/day and 2000 mg/day at bedtime were well tolerated with few side effects and produced favorable effects on the major circulating lipoproteins of patients with primary dyslipidemias as specified by the enrollment criteria.