A thyroid gland that produces too little thyroid hormone is a very common problem. The drug used to treat it, levothyroxine (Synthroid or Levoxyl), is among the most commonly prescribed medicines in the United States. But could other medicines make a thyroid problem worse? Antidepressants like sertraline may pose a problem. A surprising number of medications can interfere with thyroid function tests.
Diagnosing Thyroid Problems Can Be Harder Than It Seems:
Although doctors often believe that hypothyroidism should be straightforward to diagnose and to treat, the many different ways that thyroid hormone can affect metabolism can sometimes complicate the effort. The season of the year can also impact the functioning of the thyroid gland.
Just to make things even more challenging, some medications have an impact on thyroid hormone and could suppress it. That might be helping to make this reader’s thyroid problem worse.
Is Sertraline Making Her Thyroid Problem Worse?
Q. A few years ago my doctor prescribed sertraline for depression. I gained 20 pounds but when I complained, she attributed the weight gain to increased happiness. I do not accept that explanation.
I have been an avid exerciser since my teens and I watch my weight carefully. Believe me, I was not eating more! In addition, no matter how much I exercise, the weight stayed on.
I believe sertraline altered my metabolism. Could it have interfered with the Synthroid I have been taking for two decades for an underactive thyroid?
Another reader also wondered whether sertraline is making her thyroid problem worse:
Q. This winter I find that I have a hard time getting out of bed. My energy level is very low and I’ve gained weight. My doctor said I am depressed and prescribed an antidepressant. I don’t feel any better while taking it, though.
My only other medication is levothyroxine for hypothyroidism. Could there be an interaction between levothyroxine and sertraline?
Sertraline May Affect Thyroid Function:
A. An underactive thyroid can lead to depression or weight gain on its own. Since you have been taking the same dose of levothyroxine (Synthroid) for a long time, that might not explain your experience. It does suggest that the answer to your question might be complicated, though.
Doctors have been debating for decades whether or not the antidepressant sertraline interferes with the thyroid hormone levothyroxine. An initial report in The New England Journal of Medicine (Oct. 2., 1997) put up a red flag for this interaction.
A recent review found that the evidence for this interaction is inconclusive (Frontiers in Endocrinology, Dec. 22, 2020). However, people taking sertraline might need a higher dose of levothyroxine.
You may be caught in a vicious cycle in which sertraline makes your thyroid problem worse and reduced thyroid activity makes you feel depressed.
Do You Need More Thyroid Hormone in the Winter?
During the winter some people need more thyroid hormone than during other seasons (Journal of Clinical Endocrinology and Metabolism, June, 1982). Low thyroid activity can lead to symptoms of depression and lack of energy along with many other health problems such as weight gain.
It’s easy to chalk up such symptoms to the winter blues. The pandemic only makes matters worse. Because endocrinologists have not studied seasonal variation very much, they may not realize that winter might make someone’s thyroid problem worse. After all, a doctor may only order one annual thyroid blood test. If the results are within normal limits, it is easy to assume that all is well.
A review in Frontiers in Endocrinology (Feb. 24, 2021) offers a more in-depth understanding of thyroid fluctuations:
Lack of Awareness:
“Individuals exhibit fluctuations in the concentration of serum thyroid-stimulating hormone (TSH) over time. The scale of these variations ranges from minutes to hours, and from months to years. The main factors contributing to the observed within-person fluctuations in serum TSH comprise pulsatile secretion, circadian rhythm, seasonality, and ageing. In clinical practice and clinical research however, such within-person biological variation in serum TSH concentrations is often not considered.
“In clinical practice, the season for thyroid testing can influence a patient’s test result…”
These scientists found that TSH levels tend to be significantly higher in winter than in summer, both in people with thyroid disease and those without. Patients with hypothyroidism may find their thyroid problem worse in winter.
What to Do If Winter Makes Your Thyroid Problem Worse?
If you have your blood drawn in the spring, summer or fall, your thyroid test may suggest you are “normal.” If, however, your test is performed in January, February or March, it may reveal that your thyroid problem is worse in the winter.
In practical terms, this might mean that your dose of levothyroxine needs to be adjusted, depending upon the seasons and the function of your gland. Your doctor may not be aware of this seasonal effect. You may want to print this article and show it to your endocrinologist along with the free full text article published in Frontiers in Endocrinology (Feb. 24, 2021).
Thyroid Function Tests:
There’s one more thing! Many medications can mess up thyroid function tests. Researchers at the University of Michigan presented the their findings at the Endocrine Society’s annual meeting (ENDO 2021). They reported that roughly a third of older adults take drugs that interfere with thyroid testing.
Here is a partial list of medications that can impact testing:
- Amiodarone prescribed for irregular heart rhythms
- Corticosteroids such as prednisone or prednisolone
- Lithium prescribed for bipolar disorder
- Tamoxifen used to treat breast cancer patients
- Carbamazepine prescribed for seizure disorders and off label to treat bipolar disorder and nerve pain
Our 35-page eGuide to Thyroid Hormones explains drug interactions, symptoms, testing and treatment in far greater detail. You can find this online resource in the Health eGuides section of this website.
