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.