Osteoarthritis is the most common cause of disability and aging is the major risk factor. One of the low‐risk herbal medicines for reducing pain and inflammation in persian medicine is Pistacia atlantica gum. A triple‐blind placebo‐controlled clinical trial was performed in order to evaluate the efficacy of P. atlantica gum ointment on knee osteoarthritis in elderly people. A total of 60 patients were randomly allocated to two groups. The intervention group used 4% P. atlantica ointment and the control group used placebo, topically applied three times a day, for 8 weeks. The patients were evaluated before and after the intervention using the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) scale. There were significant differences (p < .001) between two the groups in terms of joint stiffness and pain as well as function. Within groups, regarding the effect size (EF) in joint stiffness was 2.82 and 0.74 in the Pistacia and placebo groups, respectively. Regarding pain, the effect size of the intervention and placebo groups were 3.90 and 0.99, respectively. In addition, regarding function, the effect size of the intervention and the placebo groups were 4.33 and 1.17, respectively. Therefore, it seems that topical P. atlantica is significantly better than the placebo in the old patients with knee osteoarthritis.

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