Synthroid and Weight Loss

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Synthroid is a prescription medication that works to replace a hormone naturally produced by the thyroid gland in order to regulate the body’s energy and metabolism.

It is the most commonly prescribed medication for patients with hypothyroidism.

Sufficient amounts of thyroid hormone are vital for our overall health and Synthroid ensures we receive it.

But, how does Synthroid affect our weight and can it help us slim down?

Find the answers below.

Hypothyroidism and weight gain

There is a reversible relationship between higher TSH and T3 levels in obesity and lower levels of these hormones in anorexia.

According to scientists from Germany, leptin (a hormone made by adipose cells to regulate energy balance) could be the link between TSH and a person’s weight status[1].

Weight gain or increased difficulty of losing weight is characteristic for hypothyroid patients. Indeed, a growing body of evidence confirms the link between hypothyroidism and overweight or obesity.

Thyroid hormones and body composition appear to be related primarily because hormones regulate thermogenesis, basal metabolism, and they have a major impact on glucose and lipid metabolism, fat oxidation, and food intake[2].

When thyroid gland doesn’t function properly, it can induce changes in total energy expenditure, body weight, and composition, and the body’s temperature, the evidence says. What’s more, these changes are independent of the level of physical activity.

Hypothyroidism is a common problem with thyroid and it refers to cases when the gland is unable to produce sufficient amount of hormones. Considering the fact that both hypothyroidism and overweight/obesity are prevalent, we must ask ourselves whether they can be connected in some people.

Studies show that hypothyroidism is linked to decreased thermogenesis, higher BMI, lower metabolic rate, and bigger obesity prevalence[3]. Shockingly, evidence also explains that even mild dysfunction in thyroid gland such as subclinical hypothyroidism can have a big influence on a patient’s body weight and contribute to overweight or obesity.

A study whose findings were published in the Journal of Clinical Endocrinology and Metabolism discovered that thyroid function is an important factor in body weight and even slightly elevated levels of TSH (thyroid stimulating hormone) can increase obesity prevalence[4].

The role of TSH is to tell the thyroid gland how much T3 and T4 hormones it should produce. In instances when TSH activity is too high, it usually means a patient deals with hypothyroidism.

The American Thyroid Association explains weight gain is more serious in patients with more severe hypothyroidism, compared to their counterparts. Even though the relationship between hypothyroidism and weight gain is evident, the underlying mechanisms aren’t quite clear. In a vast majority of patients, most of the extra weight is due to accumulation of water and salt.

Massive weight gain is not usually associated with hypothyroidism itself and only 5-10 pounds of body weight can be attributed to effects of the thyroid gland. Of course, it all depends on the severity of hypothyroidism[5], the American Thyroid Association adds.

Synthroid and weight loss

Synthroid, levothyroxine, is a synthetic version of hormone thyroxine (T4) produced by the thyroid gland. In hypothyroid patients, the thyroid gland produces an insufficient amount of this hormone (and T3) or doesn’t produce anything at all (see this article for more information on thyroid basics and common questions.)

The medication works to replace this naturally-produced hormone and ensure the body has sufficient levels of T4 to regulate metabolism, energy, and to prevent goiter.

The T4 requirements of an individual can change due to weight loss. One study studied the T4 requirements in obese participants with acquired hypothyroidism before and after they underwent bariatric surgery to induce weight loss. For this purpose, they enrolled 93 hypothyroid patients and discovered that weight loss led to a significant reduction of the total dose of T4.

Their findings demonstrated that reduction of the T4 dose was proportional to decrease in lean body mass[6].

Basically, the bigger the weight loss, the lower the dose is necessary.

The study whose findings were mentioned below suggests that weight loss changes requirements for T4 and dropping a few pounds can also lead to the decreased dosage of the medication.

Now, we have to wonder about the impact of Synthroid or levothyroxine on weight loss itself.

Can it help overweight hypothyroid patients slim down?

We are led to believe that treatment of hypothyroidism and getting hormones in check would help us control our weight and lose a few pounds.

The reality is different in many cases, one study found.

A group of researchers at the Boston University School of Medicine carried out a study which showed that modest weight loss after levothyroxine treatment occurs only in half of hypothyroid patients.

Scientists were surprised to discover that only a few studies looked into the relationship between levothyroxine medication and weight loss in the hypothyroid patient. This is, indeed, surprising if we bear in mind that overweight/obesity are common in hypothyroidism. One would expect more studies to be conducted on this subject.

Modest weight loss or lack of it in hypothyroid patients who receive treatment with levothyroxine isn’t only due to the drug itself. The outcome depends on the severity of hypothyroidism, treatment adequacy, and a subsequent calorie intake of an individual[7].

The Synthroid dose can depend from one patient to another and it is important to establish the right dosage. At the same time, your lifestyle matters too and whether you eat a well-balanced diet or not.

Remember, making healthier lifestyle choices isn’t only about weight management in hypothyroidism, but prevention of complications such as high cholesterol and potential cardiovascular events.

It is also important to mention that weight gain or weight loss is among a number of potential side effects of Synthroid use[8].

Of course, different people have different experiences and just because someone else may have gained weight due to the medication it doesn’t mean you will too. So, don’t let this info discourage you from trying to manage your weight if dealing with hypothyroidism and taking Synthroid.

How can Synthroid aid weight loss?

Synthroid can still be a useful ally against extra pounds for hypothyroid individuals.

Most importantly, it has a beneficial impact on parameters associated with metabolic syndrome and atherosclerosis in patients who are diagnosed with hypothyroidism.

Both health problems are strongly linked to excess body weight.

One study revealed that T4 replacement therapy with levothyroxine has favorable effects on BMI, blood pressure, and cholesterol levels.

The improvement in these parameters could contribute to reduced cardiovascular risk in this patient population[9].

It is not uncommon for hypothyroid patients to change their lifestyle and still experience weight gain due to the condition they have. Synthroid can help, but as established above, it comes down to taking the right dosage.

Weight loss that occurs due to this medication is most prominent in the early stages of treatment because your body still hasn’t adapted to the increase in metabolic rate.

As the treatment with Synthroid continues, the body adjusts to the faster metabolism and weight loss slows down. We can compare this to weight loss that occurs when we just start with a training program.

At the beginning, we notice major improvements in our appearance. Later, weight loss slows down as we get used to the same exercise routine.

Synthroid can contribute to weight loss through different factors, including:

  • Energy boost – fatigue and lack of energy are common symptoms of hypothyroidism. When you have no energy, you are less likely to get up and exercise or, at least, try to stay physically active. Synthroid ensures the body has sufficient amount of hormone T4 which has a direct impact on your energy levels. As a result, you are more likely to jog, join the gym, or do some other kind of physical activity that you used to avoid


  • Faster metabolism – as mentioned throughout the post, Synthroid ensures your body has sufficient levels of thyroid hormone T4, which regulates metabolism. Slow metabolism due to thyroid hormone insufficiency can contribute to weight gain. Intake of Synthroid increases a patient’s metabolic rate, thus aiding weight loss. After all, the golden rule of weight loss is burning or spending more calories than you consume[10]


  • Ghrelin management – ghrelin is a hormone produced by specialized cells that line pancreas and stomach. Among many functions, ghrelin also increases appetite and affects energy balance. Evidence shows that hypothyroid patients have higher levels of this hormone, which could be yet another explanation to why this condition leads to weight gain. That being said, treatment with levothyroxine normalizes ghrelin levels[11]. Normalized levels of this hormone can make you feel more satiated and you are less likely to consume way too many calories a day


  • Suppressed appetite – many patients who are prescribed with Synthroid reported decreased appetite. When you don’t feel hungry, you are less likely to munch on unhealthy snacks or crave junk food, especially late at night. This is important if we bear in mind that hypothyroid patients may experience increased appetite which leads to overeating and excessive calorie intake

Can I use Synthroid for weight loss if I don’t have hypothyroidism?

Along with the intended use of Synthroid (for hyperthyroidism), it is not uncommon for people to use it for purposes that aren’t related to this health problem.

For example, some bodybuilders use Synthroid to speed up metabolism, lose weight faster so they can bulk up their muscles. That left many people wondering if they can also use this medication to lose weight even if they don’t have hypothyroidism.

The answer is – NO. If you don’t experience problems with your thyroid and if your doctor doesn’t prescribe Synthroid, then you shouldn’t use it all. In fact, taking Synthroid to speed up metabolism and lose weight if you don’t have hypothyroidism can cause hormonal imbalance and induce negative health complications.

The best thing to do to lose weight is to exercise and adjust your diet. Don’t use Synthroid or some other prescription medications created for the different purpose to achieve your goal.

Weight loss tips for hypothyroid patients

To keep your weight in a healthy range and avoid weight gain or to drop a few pounds, hypothyroid patients should try implementing these simple tips:

  • Make exercise an important part of your lifestyle
  • Take the recommended dosage of medications and follow doctor’s instructions
  • Consume anti-inflammatory foods
  • Stay hydrated
  • Limit or avoid consumption of junk food, sugary foods, and other foods that have little to no nutritional value and abundance of calories
  • Get enough sleep
  • Connect with other people with hypothyroidism and exchange experiences, tips, etc.


Hypothyroidism induces a number of symptoms that affect our quality of life and weight gain is one of them.

While healthy individuals can just make certain lifestyle tweaks to lose a few pounds, hypothyroid patients find it difficult to do so.

Most common treatment for this condition, Synthroid, can help hypothyroid individuals lose weight, but effects depend on calorie consumption, the severity of hypothyroidism, and the dosage.


[1] Reinehr T, Isa A, de Sousa G, et at. Thyroid hormones and their relation to weight status. Hormone Research 2008;70:51-57. Doi: 10.1159/000129678

[2] Rosenbaum M, Hirsch J, Murphy E, Leibel RL. Effects of changes in body weight and carbohydrate metabolism, catecholamine excretion, and thyroid function. American Journal of Clinical Nutrition 2000 Jun;71(6):1421-32.

[3] Sanyal D, Raychaudhuri M. Hypothyroidism and obesity: An intriguing link. Indian Journal of Endocrinology and Metabolism. 2016;20(4):554-557. doi:10.4103/2230-8210.183454.

[4] Knudsen N, Laurberg P, Rasmussen LB, et al. Small differences in thyroid function may be important for body mass index and the occurrence of obesity in the population. Journal of Clinical Endocrinology and Metabolism 2005 Jul; 90(7):4019-24. Doi: 10.1210/jc.2004-2225

[5] Thyroid and weight, American Thyroid Association

[6] Fierabracci P, Martinelli S, Tamberi A, et al. Weight loss and variation of levothyroxine requirements in hypothyroid obese patients after bariatric surgery. Thyroid 2016 Apr;26(4):499-503. Doi: 10.1089/thy.2015.0473

[7] Weight loss not a certainty with hypothyroidism treatment, Medscape

[8] Synthroid side effects,

[9] Gluvic Z, Sudar E, Tica J, et al. Effects of levothyroxine replacement therapy on parameters of metabolic syndrome and atherosclerosis in hypothyroid patients: a prospective pilot study. International Journal of Endocrinology, vol. 2015. Doi. 10.1155/2015/147070

[10] Healthy Weight, Centers for Disease Control and Prevention

[11] Gjedde S, Vestergaard ET, Gormsen LC, et al. Serum ghrelin levels are increased in hypothyroid patients and become normalized by l-thyroxine treatment. The Journal of Clinical Endocrinology and Metabolism June 2008, vol. 93 no. 6, 2277-2280. Doi: 10.1210/jc.2007-2619

  1. Reply
    Laura May 7, 2019 at 2:17 am

    Desiccated thyroid is also an option if one wishes a natural yet medically recognized alternative to synthetic thyroid.

  2. Reply
    Dan Thomas December 29, 2018 at 6:06 pm

    I was put on synthroid and have steadily lost 75 pounds over six months and still going down. I’m a firm believer that there is a larger link between unwanted weight and hypothyroid than many studies suggest. I’m sure genes have a lot to do with this but as for me and my genes were sure synthroid works

    • Reply
      Thyroid Advisor January 2, 2019 at 8:42 pm

      Hi Dan,

      It is great to hear that synthroid works well for you. We hear so many stories of synthroid not working, people begin to wonder if it works for anyone at all. The truth is that it works well for most people, but for those it does not – they are often left on their own.

      I’m glad you mentioned that link between hypothyroidism and weight loss. There are many more studies being done on the relationship between these two, but I do share your belief that there is a larger link. I suspect we will see this proven more throughly in a couple years.

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