Hi & Welcome. Yes, the dose of Synthyroid seems to be inadequate. Once you start taking exogenous (replacement) thyroid hormone replacement in the form of Synthyroid which helps in proper functioning and increasing the metabolism, etc. It should therefore reduce the weight which commonly occurs in hypothyroidism (under active thyroid). However, Synthroid needs to be taken in appropriate doses regularly on an empty stomach in the morning to ensure stable well regulated thyroid status. Because if the thyroid is under - treated then it can cause weight gain or difficulty in losing weight or change of voice, thick throat, etc. To ensure the adequate dose of Synthyroid, you need to undergo thyroid function tests (TSH & Free T4,) if they are within their normal ranges, then your hypothyroid state is well controlled. In general, TSH level should be 0.4 to 2.5. Beside other causes of weight gain should be detected by appropriate lab tests to rule out Cushing s syndrome or other hormonal disorder. If everything is fine then follow a good healthy diet low in calories and do regular exercise. Hope the answers given would be useful. A feedback is appreciated.