There is a paucity of treatment options for severe acne vulgaris aside from oral isotretinoin. This randomized, vehicle-controlled, multicenter, double-blind study evaluated the efficacy and safety of combination therapy using adapalene 0.1%-benzoyl peroxide 2.5% (A/BPO) fixed-dose combination gel with doxycycline hyclate 100 mg in the treatment of severe acne vulgaris. A total of 459 participants were randomized in a 1:1 ratio to receive oral doxycycline hyclate 100 mg once daily and either A/BPO or vehicle once daily for 12 weeks. Efficacy in the A/BPO with doxycycline group was demonstrated as early as week 2 compared with the vehicle arm for total, inflammatory, and noninflammatory lesions (all P < .005). At week 12, this combination was superior to vehicle with doxycycline in reducing total, inflammatory, and noninflammatory lesion counts (an added incremental benefit of 23%, 24%, and 21%, respectively), as well as for global success and overall participant satisfaction (all P < .001). Digital UV fluorescence photography demonstrated a rapid reduction in Propionibacterium acnes in the A/BPO with doxycycline group, particularly within the first 4 weeks. These findings provide evidence on the efficacy of combining A/BPO and the oral antibiotic doxycycline in the treatment of severe acne vulgaris.