On its own, hypothyroidism (low thyroid function) can cause modest weight gain. The right dose of the thyroid hormone replacement drug levothyroxine can often aid in weight loss by normalizing thyroid hormone levels. However, if the dose is too low, you can actually gain even more weight.

What’s perhaps even more frustrating is that some people are still not able to lose excess weight even when their dose of levothyroxine is correct. Upping the dose might seem the rational solution, but this could lead to serious problems such as bone and muscle loss and irregular heartbeats (arrhythmia).

This article offers advice on what you can do if you find that you have gained weight after starting your thyroid medication.

Ensure the Right Dose

It’s important that you take the right amount of your thyroid hormone replacement drug to avoid problems like weight gain.

Some healthcare providers may only prescribe enough to get your thyroid-stimulating hormone (TSH) level into the upper end of the normal range. This may not be enough to resolve your symptoms or optimize your metabolism, though.

Many thyroid experts find that a TSH level below 2.0 is ideal for the resolution of symptoms. If your TSH is at the higher end of the reference range, talk to your healthcare provider about increasing your dose of levothyroxine.

This may be an appropriate option if you are significantly overweight or have obesity, according to a 2018 study in the journal Thyroid.

Add T3 to the Treatment Plan

Levothyroxine is a synthetic form of the thyroid hormone thyroxine, also known as T4. Once your thyroid releases T4, certain organs in your body convert it into another thyroid hormone called triiodothyronine, or T3.

Levothyroxine goes by a few different brand names, the most well-known of which is Synthroid.

T4 is largely inactive, meaning it doesn’t impact your cells, whereas T3 is active.

When your body is functioning normally, the conversion process is smooth and all you generally need is a T4 drug like Synthroid. However, in a subset of people with hypothyroidism, the conversion process is faulty and they fail to effectively convert enough T4 into T3.

In cases like this, a person may benefit from the addition of T3 to their treatment plan. The synthetic version of T3, called Cytomel (liothyronine), might normalize thyroid levels and aid in weight loss (as well as other hypothyroid symptoms, such as fatigue, hair loss, or brain fog). 

However, adding T3 to your regimen is not officially endorsed by the American Thyroid Association (ATA) as there is no strong evidence that it actually improves outcomes in people with hypothyroidism.

People seeking to become pregnant or who are pregnant should only be on levothyroxine since T3 or its combinations do not cross the placenta.

Check How You Take Your Medication

For thyroid medication to be effective, it needs to be absorbed properly by your body. Here’s how to ensure that nothing interferes with maximum absorption:

Are Compounded Formulations an Option?

Your pharmacy may be able to offer a compounded formulation of levothyroxine and liothyronine. The problem with this is that compounded formulations can be difficult to dose accurately and can sometimes lead to the overtreatment of hypothyroid (which, in turn, can lead to weight gain rather than weight loss).

  • Take your medication in the morning. Wait at least an hour before eating breakfast or drinking regular or decaf coffee or milk. Both of these can lead to poor absorption of your thyroid medications.
  • Separate your thyroid medication dose from any iron- or calcium-containing supplement you take by three to four hours. The same applies to calcium-fortified juices.
  • If you have digestive conditions such as irritable bowel syndrome (IBS) or inflammatory bowel disease (IBD), or a history of bariatric surgery, talk to your healthcare provider about Tirosint. This is a gelcap formulation containing liquid levothyroxine that can improve absorption in certain people with hypothyroidism.

Consider Natural Thyroid Hormone

Despite best efforts, some people on Synthroid and Cytomel are unable to resolve their symptoms. In such cases, a healthcare provider may prescribe natural desiccated thyroid (NDT), a natural product sold under the brand names Nature-Throid, Armour Thyroid, and others. NDT is a type of thyroid drug made from the dried thyroid gland of a pig.

There is limited research on NDT, but one study found that NDT was a safe and effective alternative to levothyroxine drugs, and resulted in more weight loss for people with hypothyroidism.

Even so, NDT is not officially endorsed by the ATA due to the lack of evidence supporting its long-term effectiveness. And because there are no prescribing guidelines in place, NDT may cause the overtreatment of hypothyroidism and, in turn, additional weight gain.