Hi, Thanks for using Healthcaremagic, Your mother in law is having underactive Thyroid (Hypothyroidism) that is why her TSH level was high. She is already on supplementation of Thyroxine and she has responded to treatment. Please continue medication as prescribed to you, if you develop any symptoms of excess of thyroid like fast heart rate, perspiration, shaking hands and sleep disturbance, you can report to treating physician and if necessary dose can be reduced. Continuation of treatment depends on cause like autoimmune hypothyroidism treatment continues for long duration often lifelong. Hope this helps. Take care. Dr.Akhilesh Dubey M.D.