What the labels cover, and what they leave out
Each US label has a part of section 6.1 on laboratory abnormalities, listing values that changed more with the medicine than with placebo. None discusses whether a standard blood panel, or a drug screen, would detect the medicine. If that matters to you, ask the laboratory or the clinician who ordered the test.
MedlinePlus, the patient site of the US National Library of Medicine, asks people on semaglutide to keep their appointments with the doctor and the laboratory, because the doctor may order tests to see how the body is responding [11]. It also explains that medicines and supplements can affect results, which is why it asks you to tell your provider everything you take before a test [13].
Checks the labels describe, brand by brand
Several warnings sections ask clinicians to monitor something. The table collects them. These are descriptions from the labels, not a testing schedule; your prescriber decides what, if anything, is measured and when.
| What is monitored | When the labels describe it | Where it appears |
|---|---|---|
| Kidney function | In people reporting side effects that could lead to fluid loss; Wegovy® and Mounjaro® add especially during dose start and increases | Wegovy® §5.5 [1], Ozempic® §5.6 [2], Rybelsus® §5.5 [3], Saxenda® §5.6 [4], Victoza® §5.5 [5], Trulicity® §5.5 [6], Mounjaro® §5.5 [7], Zepbound® §5.3 [8], Foundayo™ §5.4 [9] |
| Blood glucose | Before starting and during treatment in people with diabetes, on the weight-management labels | Wegovy® §2.1 and §5.4 [1], Saxenda® §2.1 [4], Zepbound® §5.7 [8], Foundayo™ §5.5 [9] |
| Diabetic retinopathy (an eye check, not a blood test) | In people with a history of diabetic retinopathy, watching for progression | Ozempic® §5.3 [2], Rybelsus® §5.3 [3], Wegovy® §5.8 [1], Trulicity® §5.7 [6], Mounjaro® §5.7 [7], Zepbound® §5.8 [8], Foundayo™ §5.7 [9] |
| Thyroid treatment with levothyroxine | With semaglutide tablets, which raised levothyroxine exposure by 33% in a study | Wegovy® §7.2 [1], Rybelsus® §7.2 [3] |
| Narrow-margin oral drugs such as warfarin | Because the medicine slows stomach emptying and may change absorption | Mounjaro® §7.2 [7], Zepbound® §7.2 [8], Trulicity® §7.1 [6] |
| Calcitonin or thyroid ultrasound | Not routinely: described as of uncertain value for finding medullary thyroid cancer early | Section 5.1 of each label, for example Wegovy® [1] and Mounjaro® [7] |
Amylase and lipase: the most common change
Amylase and lipase are enzymes made by the pancreas. Most labels report average increases from the start of the trials; Saxenda® and Victoza® report instead how many people had a value at least three times the upper limit of normal at some point. The figures below are as each label states them.
- Ozempic® (type 2 diabetes trials): amylase up 13% and lipase up 22%, with no such change on placebo [2].
- Rybelsus® and Ozempic® tablets: amylase up 10% and 13% and lipase up 30% and 34% on the two tablet strengths studied, not seen with placebo [3].
- Wegovy® (weight trials): amylase up 15% to 16% and lipase up 39%, not seen with placebo. In its liver disease trial, lipase above three times the upper limit occurred in 4.7% versus 1.3% on placebo [1].
- Trulicity®: lipase or pancreatic amylase up 14% to 20%, against up to 3% on placebo [6].
- Mounjaro® (type 2 diabetes trials): pancreatic amylase up 33% to 38% and lipase up 31% to 42%; on placebo amylase rose 4% and lipase did not change [7].
- Zepbound® (weight trials): pancreatic amylase up 20% to 25% and lipase up 28% to 35%, against 2.1% and 5.8% on placebo [8].
- Foundayo™ (weight trials): pancreatic amylase up 16% to 20% and lipase up 26% to 31%, against 3% and 4% on placebo [9].
- Saxenda®: 2.1% had a lipase value at least three times the upper limit at some point, against 1.0% on placebo [4]. Victoza®, in its heart outcomes trial: 7.9% against 4.5% [5].
Why a high lipase is read in context
The labels state that the clinical meaning of these rises is unknown when there are no other signs or symptoms of pancreatitis [7][8]. A raised number on its own is not a diagnosis; your clinician reads it together with how you feel.
MedlinePlus explains that a very high lipase is usually a sign of acute pancreatitis, but also that many medicines can affect lipase, and that an abnormal result does not always mean a condition needing treatment [12]. Pancreatitis itself is a separate warning on every label. If pain in the stomach area is severe and persistent, with or without vomiting and sometimes spreading to the back, the Medication Guides ask you to stop the medicine and call your provider straight away [1].
Liver tests and bilirubin
A few labels mention liver results. In the Wegovy® trial in adolescents, ALT rose to five or more times the upper limit of normal in 4 treated patients (3%) and in none on placebo; in the adult heart outcomes trial, total bilirubin at three or more times the upper limit occurred in 0.3% of people on Wegovy® and 0.2% on placebo [1].
The Saxenda® label reports ALT at ten or more times the upper limit in 0.15% of treated patients versus 0.05% on placebo, and says the link to the medicine is uncertain because other causes were not ruled out in most cases [4]. Both labels note that some rises came with other possible causes, such as gallstones [1][4].
Calcitonin and the thyroid warning
Calcitonin is a hormone that can be high in medullary thyroid carcinoma, the rare cancer behind the boxed warning on these labels. The labels say routine calcitonin checks or thyroid ultrasound are of uncertain value for spotting it early, partly because the test is not very specific, and may lead to unnecessary procedures [1][7]. A high result, if measured, calls for further evaluation [1].
Saxenda® is the label that reports calcitonin from its trials: 1.2% of treated patients ended the trial at twice the upper limit of normal or more, compared with 0.6% on placebo [4]. The separate article on the thyroid warning covers calcitonin in more detail.
Values that are expected to move
Some lab changes are part of what the medicines are meant to do. In type 2 diabetes, HbA1c, which reflects average blood sugar over about two to three months, and fasting glucose are the main trial results. Even in the Wegovy® weight trial in adults without diabetes, HbA1c fell by 0.4 points on average versus 0.2 on placebo, and triglycerides by 21.9% versus 7.3% [1].
Kidney results can move the other way when fluid is lost. The labels describe acute kidney injury, sometimes needing dialysis, mostly in people dehydrated by nausea, vomiting or diarrhoea [1][7]. MedlinePlus explains that eGFR, the usual kidney number, is calculated from creatinine together with age, sex, height and weight [15].
Tests for other medicines you take
GLP-1 medicines slow stomach emptying, which can change how tablets taken at the same time are absorbed [7]. For semaglutide tablets, levothyroxine exposure rose by 33% in a study; the US labels ask clinicians to monitor the effects of oral drugs, and the EU documents say thyroid tests should be considered [1][3][10].
For warfarin, the US tirzepatide and dulaglutide labels ask for monitoring of narrow-margin oral drugs [6][7]. The EU semaglutide document says warfarin’s INR was not affected in a meaningful way in a study, but lower INR was reported with acenocoumarol, so it recommends frequent INR checks when semaglutide is started [10]. MedlinePlus explains that the PT/INR test is how a warfarin dose is checked [14].
Before your next blood test
- Tell the person ordering the test, and the lab if asked, which GLP-1 you use and since when, along with every other medicine and supplement [13].
- Bring the dates of your last doses and of any recent dose change.
- Mention recent stomach pain, vomiting, diarrhoea or poor fluid intake, since these change how kidney and enzyme results are read [1][12].
- Do not stop a medicine before a test unless your provider tells you to [12].
- Ask what each flagged result means for you; MedlinePlus explains that reference ranges differ between labs and that a value outside the range may or may not signal a problem [13].
Ozempic®, Wegovy®, Rybelsus®, Saxenda® and Victoza® are registered trademarks of Novo Nordisk A/S. Mounjaro®, Zepbound® and Trulicity® are registered trademarks and Foundayo™ is a trademark of Eli Lilly and Company. PepLabo is not affiliated with or endorsed by Novo Nordisk or Eli Lilly and Company.
When to get help
The signs and contact information below come from this article’s sourced guidance.
Emergency
- Swelling of the face, lips or throat, trouble breathing or fainting
Contact: Emergency services
Wegovy® Medication Guide [1]
Today
- Severe stomach pain that will not go away, with or without vomiting, sometimes reaching the back
Contact: Stop the medicine and call your prescriber right away, as the guide says
Wegovy® Medication Guide [1]
- Nausea, vomiting or diarrhoea that does not go away
Contact: Your prescriber, promptly
Wegovy® Medication Guide [1]
- Changes in vision if you have type 2 diabetes
Contact: Your prescriber
Wegovy® Medication Guide [1]