Study aim: To evaluate the effects of taurine supplementation alongside methimazole on anxiety, sleep quality, fatigue, cortisol levels, thyroid hormones, blood pressure, heart rate, liver enzymes, and hematological parameters in patients with hyperthyroidism. Design: This is a randomized, double-blind, placebo-controlled, parallel-group clinical trial involving 60 patients allocated in a 1:1 ratio using variable block randomization. Participants and outcome assessors will be blinded. Assessments will be conducted at baseline and after the four-week intervention. Settings and conduct: The study will be conducted at a private endocrinology clinic in Dezful. Sixty patients will be recruited through consecutive sampling and randomly allocated to intervention and control groups after four weeks of methimazole stabilization. Taurine or placebo will be administered for four weeks, with assessments performed before and after the intervention. Participants/Inclusion and exclusion criteria: Participants will include patients aged 18–60 years with clinically and laboratory-confirmed hyperthyroidism who have received methimazole at a daily dose of 10–20 mg for at least four weeks, are able to complete questionnaires, and provide informed consent. Proposed exclusion criteria include pregnancy and severe hepatic, renal, or cardiac disease at screening. Intervention groups: Intervention group (n=30): Participants will receive oral taurine capsules at a dose of 500 mg once daily, 1–2 hours before bedtime, for four consecutive weeks, in addition to standard methimazole therapy at a daily dose of 10–20 mg. The intervention will begin after at least four weeks of methimazole treatment. Main outcome variables: The primary outcome is the change in anxiety score measured using the 7 items Generalized Anxiety Disorder questionnaire at baseline and after four weeks of intervention, with changes compared between the two groups