How many weeks after beginning 25mcg of synthroid (thyroxine) can side effects occur?

Thyroid treatment: 25 mcg of levothyroxine is a very low dose; a normal dose for hypothyroidism is typically much higher. The only side effect is taking too much (hyperthyroidism: palpitations, sweating, tremor, etc) or not taking enough (hypothyroid: fatigue, cold, etc). But such symptoms can be from other things. You need to get levels checked and talk to the doctor who initially prescribed this.

Synthroid (thyroxine): If your doctor prescribed the best dose for your thyroid disease you are unlikely to get any side effects. If you are getting side effects let your doctor know.