Long-term use of lithium can impair your thyroid gland, resulting in a condition caused hypothyroidism. Symptoms of hypothyroidism include weight gain constipation muscle weakness or cramps fatigue the doctor can do a blood test to check your thyroid function if you are having these symptoms. However, lithium use may be monitored by a healthcare provider when the benefits of giving lithium to the mother outweigh the risks to the fetus. Lithium, known as a mood stabilizer, can prevent manic symptoms of bipolar disorder in children ages 12 and older. It also acts as an antidepressant and lessens suicidal inclinations. Since these findings resulted from studies with adults, the effects are not guaranteed in those under 18. lithium is for use in adults and children at least 7 years old. Do not use lithium without telling your doctor if you are pregnant. Use an effective form of birth control, and tell your doctor if you become pregnant during treatment.