Levoxyl^® (levothyroxine sodium) is commonly recommended for people who have an underactive thyroid or other thyroid problems. This prescription medication works by boosting the thyroid hormone levels in the body. However, Levoxyl is not suitable for everyone. Potential side effects of the medication include hair loss, insomnia, and heart palpitations. You should seek immediate medical attention if you think you have overdosed on Levoxyl and have overdose symptoms, such as disorientation, seizures, or strokes.