The purpose of this clinical study is to investigate the efficacy of losartan as an antifibrotic approach in addition to a physiotherapy program in patients diagnosed with frozen shoulder. The effects of losartan use on pain intensity, shoulder joint range of motion, functional status, and pain catastrophizing level will be evaluated and compared with the outcomes of patients participating in a physiotherapy program alone.

The key questions this study aims to answer are:

• Is there a difference in shoulder functionality between frozen shoulder patients using losartan in addition to a physiotherapy program and those participating in a physiotherapy program alone?
• Is there a difference in pain intensity, shoulder joint range of motion, and pain catastrophizing level between frozen shoulder patients using losartan in addition to a physiotherapy program and those participating in a physiotherapy program alone? A total of 33 patients will be enrolled in the study. Participants will be randomly assigned to one of two groups: the physiotherapy group (PT) and the physiotherapy + losartan group (PT+L). Both groups will receive the same physiotherapy program comprising range of motion exercises, stretching exercises, strengthening exercises, and mobilization techniques. Patients in the PT+L group will additionally receive 12.5 mg of oral losartan once daily for four weeks. Clinical assessments will be conducted at baseline, at week 4, and at week 8.

A total of 33 patients diagnosed with frozen shoulder at the Orthopedics and Traumatology Clinic of Istanbul Faculty of Medicine will be included in this study. Patients will be randomly assigned to two groups using a computer-based randomization method: the physiotherapy-only group (FT) and the physiotherapy plus losartan group (FT+L). The same physiotherapy program will be applied to all patients. Both groups will receive a treatment program including range of motion exercises, stretching, strengthening exercises, and mobilization techniques. All participants will receive patient education and a home exercise program during the first session. After the exercises, a 15-minute cold application will be applied both at home and in the clinic. Patients will receive physiotherapy sessions twice a week for four weeks and will be followed for a total of eight weeks. In addition, patients in the FT+L group will receive 12.5 mg of oral losartan once daily for four weeks. All patients will be evaluated before treatment and at the 4th and 8th weeks after treatment initiation. Functional status will be assessed using the Quick Disabilities of the Arm, Shoulder and Hand questionnaire (Q-DASH) and the American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form (ASES). Pain at rest, during activity, and at night will be evaluated using the Numeric Pain Rating Scale (NPRS). Shoulder range of motion will be measured using a universal goniometer, and pain catastrophizing levels will be assessed using the Pain Catastrophizing Scale (PCS).

Inclusion Criteria:

• Adults aged 18 years or older diagnosed with frozen shoulder (adhesive capsulitis)
• Having less than 50% of range of motion (ROM) in at least one of the following shoulder movements compared to the unaffected side: external rotation, abduction, flexion, or internal rotation
• Having more than 25% loss of ROM in at least two movement planes compared to the unaffected shoulder
• Patients in stage II or III of frozen shoulder

Exclusion Criteria:

• Women who are pregnant, breastfeeding, or planning pregnancy during the study
• Patients in stage I of frozen shoulder
• Patients diagnosed with inflammatory or other types of arthritis due to autoimmune diseases affecting the shoulder
• Patients with rotator cuff pathology and/or glenohumeral arthritis
• Patients with a history of prior shoulder infection
• Patients with hypotension
• Patients who have undergone previous upper extremity surgery or plan to undergo upper extremity surgery during the study period
• Patients with allergy to losartan or its active/inactive components
• Patients taking medications known to have adverse interactions with losartan
• Patients who, in the investigator's opinion, have any medical condition, laboratory abnormality, or history that could pose risk, contraindicate participation, affect the conduct, objectives, or evaluation of the study, or prevent full participation in the study