BACKGROUND: Obesity is a major public health problem and its occurrence is markedly increasing in developed and developing countries. However, few studies have investigated the use of natural products to treat obesity. The effects of taking a combination of oxymel and Zataria multiflora Boiss. (ZM), herein referred to as Zataria oxymel (ZO), on obesity, lipid profile and insulin resistance have not yet been studied. OBJECTIVE: This study evaluates the effects of oxymel and ZO on obesity, lipid profile and insulin resistance. DESIGN, SETTING, PARTICIPANTS AND INTERVENTIONS: In this randomized, controlled, triple-blind trial, overweight patients were randomly divided into three groups and received doses of study compounds twice per day for twelve weeks. Group A received 0.75 g ZM in 10 mL oxymel in each treatment; group B received 1.5 g ZM in 10 mL of oxymel in each treatment and group C (control) only received 10 mL of oxymel in each treatment. MAIN OUTCOME MEASURES: Anthropometric parameters, including body mass index (BMI), waist circumference and hip circumference, were measured at the time of registration. Blood tests were carried out at the beginning and once again at end of the study. Blood parameters included fasting blood sugar (FBS), insulin levels, serum lipid profile (total cholesterol, triglyceride, low-density lipoprotein cholesterol and high-density lipoprotein cholesterol) and liver enzymes (aspartate transaminase and alanine transaminase). Serum creatinine was also measured at the beginning of the project and in monthly intervals for three months. The homeostasis model assessment index was calculated as fasting insulin (μIU/mL) × FBS (mg/dL)/405. RESULTS: The results showed that patients receiving ZO experienced significant reduction in waist circumference in groups A, B and C, respectively (P < 0.001) but no significant change in BMI. Group A also experienced reduction in hip circumference (P = 0.01). Groups B and C had reduction in the homeostatic model assessment of insulin resistance (P = 0.05 and P = 0.01, respectively), with no significant reduction in FBS. No effect on lipid profile, liver enzymes or serum creatinine was observed in the three groups. CONCLUSION: In this study, treatment with ZO and oxymel reduced insulin resistance, and waist and hip circumferences in overweight patients. Nonetheless, the traditional Persian use of ZO as a beverage to improve the anthropometric indices in overweight individuals still requires further research with a larger sample size. TRIAL REGISTRATION Iranian Registry of Clinical Trials Code IRCT20171220037976N1.