Weight Gain After Hyperthyroidism Treatment is Common: What to Know

With Kristien Boelaert, MD, PhD, and Reshmi Srinath, MD

After successful treatment for her overactive thyroid (hyperthyroidism), the patient (who we will call June), not only gained all excess the weight she had lost while her thyroid gland was in overdrive, but the weight continued to creep up.

This is common complaint repeated by many people who visit the discussion board on EndocrineWeb. Understandably, June was so distraught with the undesirable weight gain, so she stopped taking the medication meant to normalize her thyroid levels.

Weight gain common after antithyroid drug therapy but can be managed if discussed. Treatment for hyperthyroidism may lead to excess weight gain if not addressed early. Photo: RapidEye @ iStock

What Prompts Hyperthyroid Related Weight Gain?

"This woman had developed thyroid storm," says Kristien Boelaert, MD, PhD, associate professor of endocrinology at the University of Birmingham in the United Kingdom, and senior author of a new study focusing on weight gain after treatment for hyperthyroidism. Thyroid storm is a life-threatening condition in which body temperature, heart rate, and blood pressure often rise to dangerous levels.

These symptoms arose in “June,” landing her in the intensive care unit, Dr. Boelaert says, and required urgent medical attention. Just like this patient, many people are tempted to stop taking their antithyroid therapy with of the hope of lessening the weight gain, she says, and for those who do, the result is even worse medical complications.

In recognizing this common scenario, Dr. Boelaert and her colleagues were compelled to study the issue—exactly how much weight people typicaly gain while being treated for hyperthyroidism—and report their findings in the journal Thyroid.1

Dr. Boelaert’s team found that many people do indeed gain weight, with some developing obesity. The data gathered from this study puts concrete numbers to this adverse effect of hyperthyroid treatment. Simple awareness of how common excess weight gain may be can be a big relief for patients, Dr. Boelaert tells EndocrineWeb; knowing that weight gain can occur means patients can take proactive steps to anticipate the problem and lessen the result.

Non-Surgical Treatment for Overactive Thyroid and Weight Gain

While healthcare providers are aware that weight gain may arise after treatment, they often do not mention this outcome to patients, Dr. Boelaert says.

The usual progression, Dr. Boelaert says, is this: patients notice they are losing weight without trying and go to the doctor, at which time they learn they have an overactive thyroid. They undergo treated with antithyroid drugs or with medication plus radioactive iodine treatment (RAI).

Following treatment for hyperthyroidism, patients will observe a steady weight gain despite not changes in their eating or exercise. First, the weight will approach their normal level but then many continue experience further weight gain, reaching overweight or even obesity. As such, Dr. Boelaert set out to evaluate out just how severe the weight gain issue is in patients treated for hyperthyroidism, and what might explain this problematic result.

With Hyperthyroidism, Weight Loss than Weight Regain is Common  

The researchers turned to the Thyroid Clinic Database at the University Hospitals Birmingham National Health Service Foundation Trust to gather data on all adult patients with hyperthyroidism treated either with antithyroid drugs, radioiodine (131-I), or both. Information was collected for patients treated between 2000 and 2014 with three years of followup.1 None of the patients had a thyroidectomy—surgical removeal of the thyroid—which is another treatment option.

In all, there were 1,373 patients, ages 18 to 90 years, who were evaluated, and their weight was tracked over time. During treatment, the men, in general, gain about 17.6 pounds while the women gained a little over 12 pounds. The researchers compared the patients' weight gain with that of a matched comparison population of nearly 11,000 people who did not have an overactive thyroid.1

At the start of drug treatment, those who were diagnosed as having an overactive thyroid weighed less, on average than the comparison population, Dr. Boelaert says, which was expected. However, after treatment, the patients with hyperthyroidism were more likely than the comparison group to reach a level of obesity. In effect, men were 1.7 times more likely and women, 1.3 times more likely, to gain enough weight to be considered in the obese range.1

When compared with drugs alone, treatment that included RAI was linked with an additional gain of about 1.3 pounds. (This is included in the overall gain found, as that figure looked at all patients, with all three treatment plans, and averaged the gain).1

"Experiencing steady weight gain is the most prevalent during the first six months," after treatment, Dr. Boelaert tells EndocrineWeb, and then it may taper off somewhat. But some level of weight gain was experienced by most pateints for more than 24 months.1

From the point at which the patients sought care to the end of their treatment followup, an increased in  weight of 5% or more was measured in 65% of patients with hyperthyroidism, and more than one iin three (38%) experienced a weight gain of 10% or more over their usual body weight.1

Men gained more than women and those with overactive thyroid due to Graves' disease were more likely to gain more weight than those who had toxic nodular hyperthyroidism or those whose cause of overactive thyroid was not known.1

What Is Causing Weight Gain after Antithyroid Drug Therapy?

Dr. Boelaert still can’t say for sure why individuals who are treated with antithyroid drugs to reverse their hyperthyroidism show a tendency to gain back the lost weight plus more. "It appears something in the disease process or perhaps from the treatment makes them end up heavier." Clearly, more research is needed for us to understand the specific mechanisms behind the shift upward in body weight as a result of non-surgical treatment for overactive thyroid, she says.

Also, we know that appetite signals get disturbed when the thyroid goes out of whack, she says. When patients come in for treatment, ''lots of patients say, 'I am losing weight although I feel like am eating like a horse.'" After the antithyroid treatment begins, at least some people may continue to eat the same larger amounts that they have grown accustomed to, and this may contribute to the weight gain, she says.

Do appetite signals return to normal once treatment begin? "We don't know, but we hope to study this," Dr. Boelaert says.

She worries about the adverse effects that are associated with overweight. "People with an overactive thyroid already have an increased risk of cardiovascular disease," she explains. "If they then become overweight or obese, that is a further 'hit.''' So recognizing your increased risk for heart disease, and concerns about weight gain should be discussed with your doctor, and incorporated into your treatment plan.  

Address Weight Gain from Antithyroid Drug Therapy   

The new research is providing some valuable new information, says Reshmi Srinath, MD, director of the Mount Sinai Weight and Metabolism Management Program ,and assistant professor of endocrinology, diabetes, and bone disease at the Icahn School of Medicine in New York City; she reviewed the findings but was not involved in the research.

"It puts some numbers on a phenomenon that we have observed but haven't been able to quantify," she says of the average weight gains found among the men and women in the study.

My patients with overactive thyroid, Dr. Srinath says, are often delighted at the initial weight loss but she cautions about the chance that this trend will reverse. Knowing that weight gain is likely once the drug treatment begins to normalize the thyroid function, and that weight gain may ''overshoot" resulting in unwanted excess body weight is a key point of care to be addressed.

When she sees patients, she makes it a point to warn them of the possibility of weight gain and urges them to make necessary adjustments to their diet and especially to get regular physical activity as the best way to counter the potential for weight to creep up.

It's also very important, she says, to be closely monitored while you are under treatment. Particularly in the first 18 months, patients should be in contact with your health care team every three months, for services such as lab testing, to keep an eye on the thyroid function, which requires monitoring thyroid function levels. "We want to avoid extreme fluctuations in thyroid hormone levels, which—if out of range—could accellerate the tendency to experience weight gain," Dr. Srinath says.

Frank Discussion about Weight Changes and Heart Disease Risk Needed

Awareness of the tendency for weight gain is the first crucial step for every patient with hyperthyroidism, Dr. Boelaert says. She says doctors should be more forthcoming about the probability of weight gain but that patients should be prepared to discuss it and insist it become part of your care plan.

"I tell patients, 'When I make you better, I expect that you will gain weight. The evidence is that probably you will gain more than you lost." So know this, and advocate for clear guidance on what you can change to slow any inevitable weight gain and to prevent exceeding your usual, healthy weight.

Dr. Boelaert found slightly more higher net weight gain in her patients who had radioactive iodine therapy than drugs alone, but she doesn’t think this side effect should not steer people away from having RAI treatment since the cure is much higher with this treatment, she says.

She notices that the patients who do adopt a healthier lifestyle, if they weren’t already following a heart healthy diet and getting daily physical activity, when she first met them, can curtail the otherwise likely excess weight gain.

"Having an overactive thyroid is not a benign disease," she tells her patients. Treatment is crucial and so is keeping an eye on your weight as the treatment process progresses.

Neither Dr. Boelaert nor Dr. Srinath have any disclosures. 

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