The drugs Synthroid® and phentermine are completely different, and they are used, by prescription, for different medical indications. The only connection between Synthroid® and phentermine is that they have both been used as weight loss agents, albeit incorrectly in the case of Synthroid®. Phentermine is a weight loss agent, but is contraindicated for use in patients with thyroid problems. Synthroid® is not indicated for use as a weight loss agent and can, in fact, be dangerous if used as such.

Synthroid® and phentermine are by no means interchangeable. Phentermine is the active ingredient in a preparation used as an appetite suppressant. Synthroid® is the trade name of a drug that is used to treat hypothyroidism or low thyroid levels. Although Synthroid® might cause a loss of weight in patients with low thyroid, because of the normalizing of thyroid levels, it is not indicated for use in people with normal thyroid levels. Using it for weight loss might, in fact, be damaging.

Hypothyroidism is a condition that results because the thyroid gland not producing enough thyroid hormone. It might cause weight gain as one of its effects. Treatment with Synthroid®, which contains levothyroxine, a synthetic form of the hormone, allows replacement of the thyroid hormone and therefore normal levels of thyroid. As a result, the excess weight because of the normalization of thyroid levels might be lost.

People who have normal thyroid levels do not need to replace thyroid hormone and should, therefore, not take Synthroid®. The hormone levels in the body are finely regulated and influence each other intricately. Taking a hormone that is not medically indicated might trigger a cascade of changes in the body with possibly dangerous results. Synthroid® should be used only when medically indicated, under doctor's supervision.

The same applies to phentermine. It also is only available by prescription from a doctor. Registered for weight loss, it is indicated for use in severely obese patients. It is an amphetamine-like drug and is potentially addictive, so it should be used only in the short-term, to "kick-start" weight loss.

Phentermine works by decreasing the appetite. It might have other excitatory effects, such as hypertension and restlessness. It should be given only under strict medical supervision by a doctor who knows the patient's clinical history, any underlying diseases and other medications, because it might interact with concomitant drugs and diseases. Once phentermine is stopped, normal appetite resumes, so it is vital for patients to institute dietary and lifestyle changes while on the drug.

Essentially, the only way for a person to lose weight is by exercising more frequently and eating less. There are no quick fixes to losing weight. It does help for one to have support while trying to lose weight. Getting the help of a dietitian or nutritional therapist and enrolling at a gym where the advice of a personal trainer can be obtained is recommended.

If weight gain is suspected to be related to low thyroid levels, consultation with a doctor is recommended. Diagnosis and treatment of established hypothyroidism is simple. For more information about Synthroid® and phentermine, one should contact a licensed medical professional or pharmacist.