Objectives: Osteoarthritis is one of the most common diseases among older people which is one the most important causes of disability and heavy socio-economic burden on the elderly and society. This study aimed to investigate the effect of melilotus officinalis oil on knee joint pain and stiffness among older adults with mild to moderate primary knee osteoarthritis.
Methods & Materials: This is a double-blind randomized controlled clinical trial (registration code: IRCT2016082129461N1). Participants were 61 eligible older adults (35 females and 26 males with a mean age of 78±7.79 years) residing in one of the nursing homes in Tehran, Iran who had mild to moderate knee osteoarthritis clinically diagnosed by an orthopedic physician. Then they were assigned randomly into two groups of intervention and control received melilotus officinalis oil and diclofenac gel, respectively, using a randomization table based on balance block randomization. The data were collected using a demographic form and the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) for evaluating knee joint pain and stiffness at baseline, 2 weeks and 4 weeks after the intervention. Collected data were analyzed in SPSS V. 23 software. 
Results: There was no statistically significant different between the intervention and control groups in terms of sociodemographic variables (age, education, marital status, occupation, smoking, physical activity, chronic illness, and medication) at baseline. Knee pain (F1,58=119.07, P<0.001) and joint stiffness (F 1,58=19.9, P<0.001) reduced significantly in both groups, where the effect size was higher in the intervention group. No considerable side effect reported during the study.
Conclusion: Compared to diclofenac gel, melilotus officinalis oil can reduce knee joint pain and stiffness in older people with mild to moderate knee osteoarthritis. Therefore, it is suggested for treatment of people with knee osteoarthritis. Further studies are recommended to investigate the mechanism of melilotus oficinalis oil in reducing knee pain and stiffness and determine its effective dosage.