Researchers looked at how often doctors check thyroid levels in older adults taking a popular diabetes and weight-loss medication called GLP-1 drugs. They found that when people take these medications, they often lose weight, which can change how much thyroid medicine they need. However, doctors aren’t checking thyroid levels any more often than they do for patients on other diabetes drugs. This is a missed opportunity because these patients may need their thyroid medicine adjusted more frequently due to weight loss.
The Quick Take
- What they studied: Whether doctors are checking thyroid hormone levels often enough in older adults who start taking GLP-1 drugs (popular medications for diabetes and weight loss) while already taking thyroid medicine
- Who participated: 5,370 adults aged 65 and older with type 2 diabetes who were taking thyroid medication. About 72% were women, and the average age was 73 years. All participants were on stable thyroid doses before starting the new medication.
- Key finding: About 83% of patients in both groups had their thyroid checked within one year, with an average wait time of about 4.3 months. Importantly, doctors checked thyroid levels at the same rate whether patients were taking GLP-1 drugs or a different diabetes medication, even though GLP-1 drugs cause more weight loss and are more likely to require thyroid medicine adjustments.
- What it means for you: If you’re taking thyroid medicine and start a GLP-1 drug for diabetes or weight loss, you may want to ask your doctor about more frequent thyroid checks. While current monitoring appears adequate on average, the study suggests doctors may not be adjusting their monitoring strategy based on the greater weight loss these drugs cause.
The Research Details
This was a retrospective cohort study, which means researchers looked back at medical records from the past rather than following people forward in time. They used Medicare insurance claims data from 2011 to 2020 for adults aged 65 and older. The researchers compared two groups: people who started taking GLP-1 drugs and people who started or continued taking SGLT-2 inhibitors (a different type of diabetes medication). They matched people in both groups based on similar characteristics using a statistical method called propensity score matching, which helps make fair comparisons between groups.
The study focused specifically on people who were already taking levothyroxine (thyroid medicine) at a stable dose before starting their new diabetes medication. Researchers then tracked whether and when these patients had their thyroid hormone levels tested (TSH testing) during the following year. They used advanced statistical methods to analyze the data and identify patterns in testing behavior.
This research approach is important because it looks at real-world medical practice using actual insurance claims, rather than a controlled experiment. This tells us what doctors are actually doing in everyday practice, not just what guidelines recommend. The study design allows researchers to compare two similar groups of patients and see if their thyroid monitoring patterns differ based on which medication they’re taking. This real-world evidence is valuable for understanding whether current medical practice matches what the science suggests should happen.
This study has several strengths: it uses a large sample size (over 5,000 matched patients), includes real-world data from actual medical practice, and uses statistical matching to create fair comparisons between groups. However, there are limitations: the study only included Medicare patients aged 65 and older, so results may not apply to younger people. The study also couldn’t determine why doctors made certain testing decisions or whether they had good reasons for their timing. Additionally, the study is observational, meaning it shows what happened but can’t prove that one medication directly caused different testing patterns.
What the Results Show
The main finding was that thyroid testing patterns were nearly identical between the two groups. About 83% of patients in both the GLP-1 drug group and the comparison group (taking a different diabetes medication) had at least one TSH test within one year of starting their medication. The average time to the first thyroid test was approximately 130 days (about 4.3 months) for both groups.
This similarity is notable because GLP-1 drugs typically cause more weight loss than the comparison medication. Since weight loss can reduce how much thyroid medicine a person needs, you might expect doctors to check thyroid levels more frequently or sooner in GLP-1 patients. However, the data shows doctors were checking at the same rate regardless of which medication patients were taking.
The study included 5,370 matched patients with an average age of 73 years, of whom 72% were women. Most participants (87%) were White. All participants had type 2 diabetes and were taking a stable dose of levothyroxine before starting their new medication.
The study didn’t report major secondary findings, but the consistency of the results across both groups is itself significant. The fact that testing patterns didn’t differ suggests that doctors may not be adjusting their monitoring strategy based on the different weight-loss effects of these medications. This indicates a potential gap between what medical science suggests should happen and what actually happens in practice.
This study adds to existing knowledge about how GLP-1 drugs affect people already taking thyroid medicine. Previous research has shown that weight loss from any cause can reduce thyroid hormone requirements, potentially leading to too much thyroid medicine in the bloodstream if doses aren’t adjusted. This study is one of the first to examine whether doctors are actually monitoring thyroid levels differently when patients start GLP-1 drugs, which are known to cause significant weight loss. The findings suggest that current practice may not fully account for this important difference.
The study only included Medicare patients aged 65 and older, so the results may not apply to younger people taking these medications. The study couldn’t determine why doctors ordered tests when they did or whether they had specific clinical reasons for their timing decisions. The study also couldn’t measure whether patients actually lost weight or how much, only that they were prescribed these medications. Additionally, the study looked at insurance claims data, which may not capture all thyroid testing (for example, tests done at certain clinics might not be recorded). Finally, this is an observational study, so it can show what happened but can’t prove that the medication itself caused the testing patterns observed.
The Bottom Line
If you’re taking thyroid medicine and your doctor prescribes a GLP-1 drug for diabetes or weight loss, consider asking your doctor about thyroid monitoring. The evidence suggests that thyroid checks within the first year are common (about 83% of patients), but you may benefit from checking sooner or more frequently given the weight loss these drugs typically cause. This recommendation is moderate confidence, as the study shows current practice is reasonable but may not be optimal. Always follow your doctor’s specific recommendations for your situation.
This research is most relevant to adults aged 65 and older with type 2 diabetes who take thyroid medicine and are considering or starting GLP-1 drugs. It’s also important for doctors prescribing these medications to patients on thyroid medicine. Younger people taking these medications should also be aware of this issue, though this study didn’t specifically examine them. People taking thyroid medicine for other reasons (like hypothyroidism from Hashimoto’s disease) should also be aware that weight loss from any cause can affect thyroid medicine needs.
If you start a GLP-1 drug, significant weight loss typically begins within the first few weeks to months. Thyroid medicine adjustments may be needed within 2-3 months as weight loss occurs. The study found that most patients had their thyroid checked within 4-5 months, but earlier checking (around 6-8 weeks) might be more appropriate given the typical timeline of weight loss with these medications.
Want to Apply This Research?
- Track your weight weekly and note the date you start any new diabetes or weight-loss medication. Set a reminder to schedule a thyroid test 6-8 weeks after starting the medication, and track the results when you receive them. Record any symptoms like fatigue, heart palpitations, or mood changes that might indicate thyroid medicine needs adjustment.
- Use the app to set a calendar reminder for thyroid testing 6-8 weeks after starting a GLP-1 medication. Create a checklist of questions to ask your doctor about thyroid monitoring frequency. Log your weight weekly to track progress and share this data with your healthcare provider to support discussions about thyroid medicine adjustments.
- Set up monthly weight tracking in the app and quarterly thyroid test reminders. Create a symptom log to record energy levels, heart rate changes, and mood to help identify when thyroid medicine adjustments might be needed. Share this data with your doctor at regular check-ins to ensure your thyroid medicine dose stays appropriate as your weight changes.
This research describes current medical practice patterns and does not constitute medical advice. If you take thyroid medicine and are considering or taking GLP-1 drugs, consult with your healthcare provider about appropriate thyroid monitoring for your individual situation. Do not change your thyroid medication dose without medical supervision. This study was conducted in Medicare patients aged 65 and older and may not apply to younger individuals. Always work with your doctor to determine the best monitoring schedule for your specific health needs.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.