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December 01, 2022 6 min read

When you think of weight gain, you probably don't think of levothyroxine. After all, shouldn't thyroid medication help aid in weight loss? Well, in a perfect world, it does. But the truth is a synthetic thyroid hormone like levothyroxine can cause some people to pack on the pounds. This might seem paradoxical, but it's actually a pretty common side effect.

So how does this medication cause weight gain, and what can you do to counteract the effect? Keep reading to find out!

What is levothyroxine?

Levothyroxine is a synthetic form of the thyroid hormone thyroxine (T4), which is naturally produced by the thyroid gland. The medication treats hypothyroidism (underactive thyroid), a condition in which the thyroid gland doesn't produce as much hormone as it should. It's also used to treat a thyroid disease called a goiter, as well as for thyroid cancer patients who underwent thyroidectomy.

Sometimes, this medication is also used to suppress your levels of thyroid-stimulating hormone (TSH), which is a hormone produced in the pituitary gland. The medication replaces the missing thyroxine in the body and helps regulate metabolism.

What is levothyroxine?

What's the connection between levothyroxine and weight gain?

Before we discuss how levothyroxine can affect weight, you must understand the connection between underactive thyroid and weight. Weight gain is one of the most common symptoms of hypothyroidism. 

Normal thyroid hormone production aids in your metabolism or your body's ability to burn fat for energy. It also supports your liver and pancreas' ability to digest stored calories for use as fuel. Additionally, your thyroid hormones also help your muscles as they use energy. When your thyroid gland doesn't produce as much hormone as it should, these systems can be impaired. 

Thus, your metabolism slows down, so your body holds on to calories and stores them as fat, which is difficult to break down. In simple words, with hypothyroidism, your body won't be able to burn off calories and break down fat as quickly as it should. Plus, you'll have little energy and feel sluggish, making it especially difficult for you to exercise. Many hypothyroid patients may also experience some fluid retention. All of these things can cause you to pack a few more pounds.

So, what's the effect of levothyroxine on your weight?

Again, levothyroxine replaces the missing hormone, helping your body regulate metabolism. Therefore, it may ease some symptoms of underactive thyroid. Thus, it may aid in weight loss. According to the American Thyroid Association, you may lose up to 10% of your weight after you start this medication. In most cases, you'll return to your normal, pre-hypothyroidism body weight.

It's important to note, however, that this medication has another effect besides helping you lose weight. This brings us to the next question…

Does levothyroxine make you gain weight?

Surprisingly, the answer is yes. Among the many levothyroxine side effects, weight gain is pretty common. But how can it cause you to gain weight? Isn't it designed to improve your metabolism and aid in weight loss? Shouldn't you be losing weight instead of gaining? There are several answers to this question.

The first answer is undertreatment. When your dose is too low, you may still experience weight gain because your body still doesn't have enough thyroid hormone levels to function normally. The next answer is poor absorption of the medication. Poor absorption means you won't get the total dosage, so you may not experience the desired relief hypothyroid signs like weight gain from hypothyroidism. 

The last answer is a little paradoxical: you might take too much levothyroxine. The reason lies in the T4 to T3 conversion and how this medication is utilized in your body. Remember that T4 is the inactive hormone, while T3 is the active one

Levothyroxine only contains T4. By itself, T4 doesn't really do anything for your body. For it to be active and useful, your body needs to convert it to the active hormone T3. But the problem is that not everybody can do this conversion properly. Sometimes, instead of turning T4 into T3, your body converts T4 into rT3 (Reverse T3). rT3 is a metabolite of T4 that has little biological activity. It can completely block your thyroid T3 activity, lower your metabolism, and make you more hypothyroid. And, of course, it may result in weight gain. 

Taking levothyroxine, especially in a high dose, when your body can't do the conversion well, may only whack the ratio of T3 to rT3. This is because your body can only make rT3 when T4 is present, so adding more T4 can result in more rT3. In most cases, however, poor T4 to T3 conversion might still cause weight gain even when you take the right amount.

How can you avoid weight gain on levothyroxine?

If you're taking levothyroxine and start gaining weight, don't freak out. It might feel like the end of the world, but there are solutions to help you manage your weight. 

Take the right dose

When your dose is too low, you might still experience weight gain because your thyroid hormones are still not in their normal range. However, taking too much is also not a good idea. As explained before, then your body can't convert T4 to T3 properly, and the side effect is paradoxical. In this case, the more you add T4 into your body, the worse your hypothyroidism will be. 

So what if your body has no problem converting T4 to T3? Can a higher dose help you lose more body weight?

When the conversion is normal, and your dose is too high, you'll have too much thyroid hormone in your body. This will cause you to experience hyperthyroidism or overactive thyroid. While losing weight is one of the side effects, it's dangerous. Therefore, taking the correct dose is essential.

Your doctor will likely start with a lower dose and gradually increase it until you feel your best. They may also require you to do regular thyroid lab tests like blood tests to help adjust your dose.

Boost your T4 to T3 conversion

If T4-only medication causes you to gain weight because your body can't convert T4 to T3 correctly, you might want to look for ways to boost the conversion. One way to do it is by ensuring that your body has all the right nutrients that support proper conversion. 

Iodine and selenium are two essential nutrients for your thyroid function. Both work harmoniously to ensure that the conversion of T4 to T3 is optimal. Therefore, getting these two nutrients in your diet is crucial. You might want to ensure that you get enough zinc, vitamin A, and vitamin D since they're good for your thyroid health. Aside from 

In addition to your diet and eating habits, managing stress levels is important. Stress can impact the conversion of T4 to T3, so finding ways to manage stress levels is vital. Chronic stress can increase the hormone cortisol, which can interfere with the conversion process. Another important thing you need to do to is getting an exercise routine. By boosting your thyroid function and hormone conversion, weight loss will likely be easier.

Change your medication

A lot of people don't realize that sometimes, the best option when it comes to thyroid medication is to change it up. This is especially true if your body can't convert T4 to T3 properly. In this case, it may be best to switch to a natural desiccated thyroid (NDT), such as Armour Thyroid and VitaliThy.

This medication is derived from pig thyroid glands and contains the natural form of both T3 and T4 hormones. What's great about it is that it more closely resembles the hormone levels in a healthy human thyroid. This can be beneficial because it allows your body to more efficiently utilize the hormones as the medication doesn't rely exclusively on the conversion.

Furthermore, VitaliThy doesn't only contain T4 and T3 but also other thyroid hormones present in human thyroid glands, such as T2, T1, and Calcitonin. Plus, it's natural, gluten-free, and lactose-free, making it especially great for those who want to avoid potential allergens.

But why don't doctors prescribe NDT? Well, generic levothyroxine, along with Synthroid (its brand name counterpart), are the most common medications to treat hypothyroidism because they're considered the "safest" option. But there's also a business reason behind this: synthetic T4 medication is cheaper to manufacture and more profitable. In reality, it's not necessarily more effective or safer than NDT.

In fact, a study of 70 hypothyroid patients showed that most people preferred NDT over levothyroxine because it provides better relief from hypothyroid symptoms. NDT is also associated with more weight loss. 

If you can't seem to lose weight while taking levothyroxine, consider giving VitaliThy a try. It just might be the best thing for you!


Wojciech Majda
Wojciech Majda

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