To determine the efficacy of wet-cupping for treating persistent nonspecific low back pain. Wet-cupping therapy is one of the oldest known medical techniques. It is still used in several contemporary societies. Very minimal empirical study has been conducted on its efficacy. Randomized controlled trial with two parallel groups. Patients in the experimental group were offered the option of referral to the wet-cupping service; all accepted that option. The control group received usual care. Medical clinic in Kermanshah, Iran. In total, 98 patients aged 17-68 years with nonspecific low back pain; 48 were randomly assigned to experimental group and 50 to the control group. Patients in the experimental group were prescribed a series of three staged wet-cupping treatments, placed at 3 days intervals (i.e., 0, 3, and 6 days). Patients in the control group received usual care from their general practitioner. Three outcomes assessed at baseline and again 3 months following intervention: the McGill Present Pain Index, Oswestry Pain Disability Index, and the Medication Quantification Scale. Wet-cupping care was associated with clinically significant improvement at 3-month follow-up. The experimental group who received wet-cupping care had significantly lower levels of pain intensity ([95% confidence interval (CI) 1.72-2.60] mean difference=2.17, p<0.01), pain-related disability (95% CI=11.18-18.82, means difference=14.99, p<0.01), and medication use (95% CI=3.60-9.50, mean difference=6.55, p<0.01) than the control group. The differences in all three measures were maintained after controlling for age, gender, and duration of lower back pain in regression models (p<0.01). Traditional wet-cupping care delivered in a primary care setting was safe and acceptable to patients with nonspecific low back pain. Wet-cupping care was significantly more effective in reducing bodily pain than usual care at 3-month follow-up.