The medication Levothyroxine is known to cause both weight gain and weight loss, but it is more common for the medication to cause the patient to lose weight, according to the website Drugs. Taking normal doses of Levothyroxine should not cause weight loss, and it is not recommended to take the medication for weight loss because taking too much of it can be fatal.
Levothyroxine helps treat hypothyroidism by replacing or providing more thyroid hormones. Hair loss is one of the most common side effects associated with taking this medication. Other side effects include extreme fatigue, menstrual changes, irregular breathing, decreased urine output, irritability and difficulty breathing. Symptoms of an underactive thyroid include changes in consciousness, confusion and cold and clammy skin, as stated by WebMD.