Abstract: Background: Acne vulgaris is self-limiting, multifactorial disease involving sebaceous glands. Omeprazole is a proton pump inhibitor with in vitro antibacterial effects against staphylococcus aureus and anti-androgen that can be potential treatment of acne vulgaris. This study was designed to evaluate the efficacy of oral omeprazole and erythromycin 4% compared to doxycycline combination therapy in the treatment of acne vulgaris. Methods: In this clinical trial study, patients with moderate acne were referred to Skin Diseases and Leishmaniasis Research Center, Isfahan University of Medical Science, Iran, during August 2014 until November 2015 and were randomized into two groups receiving topical erythromycin 4% plus omeprazole (34 patients) or doxycycline (35 patients) for 3 months. Moderate acne, lack of sensitivity to proton pump inhibitors, lack of warfarin, phenytoin, diazepam consumption, lack of active liver or kidney disease, being older than 12 years, were considered as inclusion criteria. Pregnant or lactating patients, patients with drug allergy history, patients taking oral contraceptives, acne topical medications (including retinoids) or systemic treatment within 30 days of study, patients with oligomenorrhea, hirsutism, acne conglobata, acne fulminant or body acne alone were excluded from the study. All patients were tested for Helicobacter pylori test at the beginning of the study. Results: Both inflammatory and non-inflammatory lesions decreased in both groups with negative correlation with age (P< 0.05). There was no significant correlation between positive Helicobacter pylori test and inflammatory or non-inflammatory lesion reduction (P= 0.794, P= 0.514). Also, patient satisfaction and rate of total drug side effects was not different between two treatment groups. Rate of skin reactions was 20.58% in omeprazole treated group and 11.42% in doxycycline group. For side effects, other than skin it was 2.94% versus 14.28% respectively. Conclusion: Omeprazole could be suggested as an alternative for doxycycline in the treatment of patients with moderate acne vulgaris especially in non-inflammatory lesions
