Synthroid®, or levothyroxine sodium, is a prescription drug used to treat hypothyroidism, in which the body does not produce sufficient levels of thyroid hormone. Synthroid® acts as a synthetic replacement for the body's own thyroid hormone. The connection between weight loss and Synthroid® is that the prescription drug often causes weight loss, because hypothyroidism causes the body's metabolism to slow, and frequently causes weight gain. When the hypothyroidism is treated, theoretically, the additional weight that was gained will be lost; it is often more complicated than that, however, and some people even end up gaining weight on the drug.
The specific dosage of Synthroid® is carefully determined based on the patient's existing weight and thyroid hormone levels, and is then adjusted as needed. This means that weight loss and Synthroid® use are carefully monitored by a doctor to ensure that too much of the drug is not given, which could push the patient into hyperthyroidism. This could potentially cause an irregular heartbeat as well as increased hunger and thirst; though it is less common that a hyperthyroid patient would gain excess weight, it is possible if the hyperthyroidism is caused by a prescription imbalance.
People with thyroid conditions will likely need to manage the condition for their entire lives with medication. Weight loss is to be expected with Synthroid® use, and so many patients need their prescription levels to be adjusted based on their changing weight as the condition is treated. Managing a healthy weight and lifestyle can make it easier to control a thyroid condition and keep thyroid hormones in the blood within normal levels. Regular bloodwork is required to be certain that the Synthroid® is maintaining the levels correctly; there are other prescription drug options to manage thyroid levels, as well, if Synthroid® is ineffective.
Weight loss and Synthroid® use are only indicated when the drug is used to treat hypothyroidism and is carefully monitored by a physician. Synthroid® should never be used to simply boost metabolism and encourage weight loss for any other reason, because it is possible to overdose on the drug and cause permanent damage to the body. A reputable doctor will not prescribe Synthroid® simply to encourage weight loss or to burn excess fat. In addition, the connection between weight loss and Synthroid® use is not always guaranteed, and some people find that they do not lose any weight while taking the drug.