This study investigated the effect of St. John's Wort oil on pain intensity and physical functions in people with knee osteoarthritis. This study adopted a randomized, placebo-controlled, and qualitative mixed design. The sample consisted of 60 patients randomized into intervention (n=30) and placebo control (n=30) groups. The experimental group participants were treated with St. John's Wort oil three times a week for three weeks, while the placebo control group participants were treated with olive oil three times a week for three weeks. Quantitative data were collected using a patient identification form, the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), and the Visual Analogue Scale (VAS). Qualitative data were collected through semi-structured interviews. .

This study adopted a randomized, placebo-controlled, and qualitative mixed design. Qualitative data were collected using a semi-structured interview questionnaire.

The study was conducted in the physical therapy and rehabilitation outpatient clinic of a public hospital in Türkiye. The study population consisted of all patients admitted to the outpatient clinic for osteoarthritis-related pain. The data collection process continued from December 2017 to August 2018 and was reported in accordance with the Consolidated Standards of Reporting Trials (CONSORT) guidelines. A pilot study was conducted with five patients before data collection.

Patients diagnosed with osteoarthritis by a physical therapy and rehabilitation specialist according to ACR criteria were randomized into the study by the University Biostatistics Unit. The initial sample consisted of 72 patients divided into intervention (n=36; St. John's wort oil) and placebo control (n=36; olive oil) groups. However, six experimental group participants were excluded because they either could not be contacted on the phone during the follow-ups (n=4) or stated that they would be out of town for a long time (n=2). Six control group participants were also excluded because they either could not be contacted on the phone during the follow-ups (n=3), did not want to keep up with the intervention (n=1), or wanted to withdraw from the study (n=2). Therefore, the final sample consisted of 30 experimental and 30 control group participants.

Inclusion Criteria:

• being literate,
• planning no pregnancy during the study,
• not being pregnant,
• having been diagnosed with knee osteoarthritis according to ACR (American College of Rheumatology),
• having had knee pain for the past month,
• needing analgesics for more than 15 days in a month,
• having osteoarthritis-related knee pain despite routine treatment with analgesics,
• having a VAS score of ≥ 4 on one knee,
• speaking Turkish,
• having no communication problems, and
• volunteering

Exclusion Criteria:

• Pregnant,
• Having a physical disability in the area where the application will be made,
• Having any skin disease in the area to be treated,
• Having large scar tissue in the area to be treated,
• Having a history of physical trauma in the last three months in the area to be treated,
• Having any peripheral vascular disease in the area to be treated,
• Having inflammatory joint disease,
• Having a history of rheumatoid arthritis and fibromyalgia,
• Using any complementary and integrative (integrated) health application in the last three months,
• Those who have undergone intra-articular treatment in the last three months,
• Receiving pain blocking treatment in the last year,
• Receiving physical therapy in the last three months and during the application,
• Patients with 2 or more pain in the other knee according to the VAS scale were not included in the study.

Patients diagnosed with osteoarthritis by a physical therapy and rehabilitation specialist according to ACR criteria were randomized into the study by the University Biostatistics Unit.