Synthroid, being a medication for the thyroid gland, is sometimes used as an unofficial weight loss aid for bodybuilders or just overweight people who are trying to lose weight. It is presented on occasional forums as an option to be looked into in case of an improperly functioning thyroid gland. However, a number of bodybuilders aren't paying adequate attention to the cautionary warning in the latter half of that statement, and are using the supplement as an aid to reduce weight and burn fat. While levothyroxine is not a steroid, the misuse of levothyroxine does not make it without consequence to a user's health. But first let’s see what levothyroxine is.
Levothyroxine (the brand name is Synthroid) is a synthetic thyroid compound chemically identical to the Thyroxine (T4). Thyroxine is an endogenous hormone secreted by the thyroid gland, and converted to its active metabolite L-triiodothyronine (T3). Thyroxine and L-triiodothyronine increase basal metabolic rate, regulate neural maturation and long bone growth, affect protein synthesis, and increase sensitivity to catecholamines. Deficiency of thyroid hormones (hypothyroidism) is linked to slowed metabolism, forgetfulness, depression, constipation, dry skin, and overweight. Symptoms can be variable and non specific, which makes it difficult to link the symptoms together as an indicator of a single problem without professional diagnosis.
Synthroid is a synthetic hormonal replacement that is commonly used to treat hypothyroidism. However, excessive quantities of levothyroxine can result in a condition called thyrotoxicosis, an artificially induced version of hyperthyroidism. Increased appetite, nervousness, restlessness, heat intolerance, fatigue, high blood pressure, menstrual irregularities, rapid heartbeat, irritability, sleeping problems, and weight loss are all the indicators of thyrotoxicosis.
Yes, weight loss is listed there. It can be among the effects of using Synthroid, but don't get too excited. While initially the words "weight loss" seem like a positive, part of this weight loss comes as the result of the body going into what is referred to as a catabolic state, a condition where the body begins breaking down muscle tissue. A natural part of the human body's survival mechanism, a catabolic state reduces the body's caloric needs by freeing up the proteins in (what the body views as) unnecessary muscle mass for other uses. It comes about naturally when the body is undergoing starvation.
It’s worth noting that levothyroxine has never been approved by the FDA for weight loss use, and just from the above information it's easy to see why. Most notably, however, is that levothyroxine is not recommended for people who have experienced heart complications such as tachycardia, acute myocardial infarction (heart attack), or ischemia. Combined with its potential catabolic effects and the increased risk of osteoporosis, Synthroid becomes a potentially dangerous drug to start taking without doctor’s approval.
Overuse of thyroidal replacement hormones can have a deleterious effect on the thyroid itself. Even when a proper dosage has been established, it's strongly advised to annually check thyroidal function in case of a need for adjustment. Overdose symptoms include headache, leg cramps, chest pain, shortness of breath, rapid heartbeat, tremors, and irritability or anxiety.
Levothyroxine is a medication meant for treatment of thyroidal deficiencies. Its use can have problematic side effects even when properly adjusted for its intended use. Improper dosage, self dosage, diet, and inconsistencies in taking the same dosage daily can all lead to serious problems. Diet especially can affect the body's absorption of levothyroxine. Foods with significant amounts of iron, calcium, magnesium and aluminum containing antacids, colestipol, simethicone, soy, and more can all reduce the effectiveness and absorption of levothyroxine.
Considering that most people who self medicate are seldom fully aware of all potential interactions, this is therefore an increased risk factor for self medicating, given that a minor change in diet can result in a drastic effect on how the body responds to the supplemental hormone.
Ultimately, Synthroid is not intended as a weight loss aid, and should not be used as one regardless of what initial "success" is achieved. Hormone replacement drugs are often taken for life and have long lasting effects on the user. For those suffering from hypothyroidism, the effects are mostly positive. For people whose thyroid gland functions properly, the effects might be unpredictable in the future.