A multicenter, 12-week, randomized, double-blinded, placebo-controlled, dose-ranging study was conducted in 233 subjects with moderate to severe facial acne vulgaris to determine the lowest effective once-daily oral dose of a new extended-release (ER) minocycline hydrochloride formulation with the safest adverse effect profile. Subjects randomly were assigned to treatment with daily dosages of ER-minocycline 1-, 2-, or 3-mg/kg tablets, or daily placebo tablets, for 84 days. At the end of the 12 weeks, the number of inflammatory lesions decreased approximately 50% from baseline levels in the dose groups. No dose-dependent effect was observed, with the percentage decrease in the number of inflammatory lesions in the 1-mg/kg treatment group being equal to or greater than higher doses. The pairwise difference between the ER-minocycline 1 mg/kg and placebo groups in the percentage decrease in inflammatory lesions was statistically significant (P = .015). Acute vestibular adverse events (AVAEs) appeared to be dose proportional, with the incidence being similar in the lowest (1 mg/kg) dosing group (24%) and in the placebo group (26%). Higher-dose regimens were associated with a higher incidence of central nervous system side effects and AVAEs. A 1-mg/kg daily dosage of the new ER-minocycline formulation is the lowest effective dose with the safest side effect profile, with higher-dose regimens offering no substantial therapeutic advantages.