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How Long After Starting Thyroid Medication Will I Lose Weight?

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a young woman is examined by a doctor,How Long After Starting Thyroid Medication Will I Lose Weight
Tetiana Tereshchenko post Reviewer Tetiana Tereshchenko post Reviewer
Sports Medicine Doctor, Dietitian, Ph.D. in Physiotherapy and Sports Medicine, Healthcare Administration Specialist

How long after starting thyroid medication will I lose weight? The answer depends – find out what you can expect from thyroid medication.

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Hypothyroidism is a condition in which your thyroid is underactive. An underactive thyroid can lead to many symptoms, including weight gain. 

Thyroid medications like levothyroxine (Synthroid) can help or resolve many symptoms associated with hypothyroidism, including weight gain. In this article, we discuss the correlation between thyroid medication and weight loss to help you determine what you can expect when starting your treatment.

Thyroid Medication and Weight Loss

Hypothyroidism happens when your thyroid does not produce enough thyroid hormones. Thyroid hormones, such as T3 and T4, play an important role in your body’s metabolism. [1]

Likewise, hypothyroidism can cause weight gain along with other symptoms, including the following:

  • Fatigue
  • Muscle and joint pain
  • Depression
  • Thinning or dry hair
  • Abnormal menstrual periods
  • Sensitivity to cold
  • Low heart rate
  • Fertility issues

Fortunately, you can treat hypothyroidism with medication. The available medications work to replace hormones that your thyroid has difficulty making. Levothyroxine is a thyroid medication that mimics a natural thyroid hormone known as thyroxine. It is available under the brand names Synthroid, Levoxyl, and Tirosint. [2]

Hypothyroidism and Weight Gain

As aforementioned, hypothyroidism is linked to weight gain. [3] Thyroid hormones control your metabolism, so in the absence of those hormones, your metabolism becomes dysregulated. 

There are two main reasons for weight gain with underactive thyroid:

  • Slowed metabolism. Experts measure your metabolic function using the basal metabolic rate (BMR). Those with hypothyroidism typically have a low BMR. This occurs because the body reduces energy production and, therefore, uses fewer calories for daily functioning.
  • Excess salt and water. Hypothyroidism is not entirely related to an increase in fat. It is more so due to salt and water retention. Because of this, those with hypothyroidism may have an excess of five to ten pounds of body weight, depending on the severity of the disease.

Will I Lose Weight Once I Start Taking Thyroid Medication?

Because hypothyroidism is linked to weight gain, you may be wondering how to lose weight with thyroid medication and if the medication really has anything to do with that. 

Treating hypothyroidism with medication will almost definitely treat related symptoms such as salt and water retention and decreased metabolism. [3] [4] Therefore, with the resolution of these side effects, you can expect a small decrease in weight. 

Typically, individuals will lose 10 percent of their body weight or less. This reduction is likely to return individuals to their baseline weight before hypothyroidism started.

One study evaluated the effects of levothyroxine treatment on weight. It enrolled 101 individuals with hypothyroidism, and by the end of the trial, 52% of the subjects lost weight, with an average weight loss of around eight to ten pounds. [5]

While some participants experienced weight loss, almost half of them didn’t. Additionally, the researchers concluded that the weight change was not significant. 

Although you may experience some weight reduction, it may not bring you to a normal BMI or your desired weight.

Because of these potential effects, let’s explore how long before Synthroid helps with weight loss.

How Long After Starting Thyroid Medication Will I Lose Weight?

You may be wondering, “How long does Synthroid take to lose weight?” and here is what you should know about that.

Weight loss on thyroid medication is not instantaneous. When you notice weight loss depends on how long it takes you to reach a therapeutic dose.

According to the levothyroxine prescribing instructions, your provider will adjust your dose every four to six weeks. [6] Therefore, it may take several weeks or months to get an effective dose. 

When you get a therapeutic dose of levothyroxine, it starts working immediately. [7] However, the resolution of symptoms can take multiple weeks before you see a difference. 

Because it takes a bit to get the dose right and for symptoms to improve, some individuals may experience weight loss within a few weeks, while it may take months for others.

In the previously mentioned study, weight loss with hypothyroidism medication occurred in half of the participants, and they lost weight by an average of eight pounds. This eight-pound measurement was collected after a period of five months of treatment. [8] Likewise, it may take several months before noticing a change in weight.

Thyroid Medication Is Not Weight-Loss Pills

Although thyroid medication can cause a small reduction in weight, thyroid medicine is not a weight-loss pill.

After analyzing the available research, we can assert that thyroid medication weight-loss success is minimal. Thyroid medication will only treat excessive weight related to slowed metabolism and excess salt and water retention.

If you start thyroid medication, any related symptoms may resolve, and your thyroid hormones may normalize. However, if you still have excess weight, it is likely that there are other factors contributing to weight gain. [3]

There are many things that can cause weight gain, and it can develop over extended periods. Under these circumstances, implementing a well-balanced diet, calorie deficit, and regular exercise will be important to achieving a healthy weight. Additionally, a weight-loss app is a great way to track your progress and manage your weight-loss goals.

Thyroid medication is only meant to treat thyroid disorders. Some evidence exists showing that high levels of thyroid hormones can cause additional weight loss versus just dieting.

However, just like laxatives or vitamin B12 shots, it is not a one-stop weight-loss drug. Using thyroid medication as a weight-loss solution can cause several adverse effects. They include heart problems, bone loss, and muscle protein loss. Additionally, if you were to stop the medication, you would regain the lost weight.


So, will thyroid meds help you lose weight? In summary, here are a few key points when it comes to hypothyroidism medication and weight loss:

  • Hypothyroidism refers to an underactive thyroid.
  • An underactive thyroid can lead to many symptoms, including weight gain.
  • Weight gain from hypothyroidism is due to a decrease in basal metabolic rate as well as salt and water retention.
  • You can treat hypothyroidism with levothyroxine, which acts like your body’s natural thyroid hormones.
  • Thyroid medication weight-loss results are modest and happen due to a reduction in salt and water in your body and an increase in basal metabolic rate.
  • Thyroid medication is associated with a decrease of 10 percent or less in body weight.
  • To treat weight gain not due to an underactive thyroid, implement a healthy diet, exercise, and a calorie deficit.
Disclaimer This article is intended for general informational purposes only and does not address individual circumstances. It is not a substitute for professional advice or help and should not be relied on to make decisions of any kind. Any action you take upon the information presented in this article is strictly at your own risk and responsibility!

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