When it comes to medications like semaglutide (Wegovy®, Ozempic®) or tirzepatide (Zepbound®, Mounjaro®), your healthcare provider doesn’t just guess which one might work best — they look at your unique health profile, which often starts with lab testing. There are a range of lab tests for semaglutide or tirzepatide that your doctor will run after they have determined if you qualify for weight loss medication.
The right lab work can reveal how your body is functioning now, what risks you may face, and which medication might offer the most benefits with the least side effects. This is especially important for patients seeking help with weight management, type 2 diabetes, or metabolic issues. Learn which lab tests are commonly used to help decide if semaglutide, tirzepatide, or another weight loss medication is right for you.
Active Ingredient: Semaglutide
Semaglutide is a GLP-1 receptor agonist only. It mimics the hormone GLP-1, which helps regulate blood sugar and appetite.
| Brand Name | Manufacturer | Route | FDA-Approved Use | FDA Approval Year |
|---|---|---|---|---|
| Ozempic | Novo Nordisk | Injectable (weekly) | Type 2 diabetes; Cardiovascular risk reduction | 2017 |
| Wegovy | Novo Nordisk | Injectable (weekly) | Chronic weight management | 2021 |
| Rybelsus | Novo Nordisk | Oral (daily tablet) | Type 2 diabetes | 2019 |
Active Ingredient: Tirzepatide
Tirzepatide is a dual agonist — it activates GLP-1 receptors and GIP (glucose-dependent insulinotropic polypeptide) receptors. The added GIP activity may enhance weight loss and blood sugar control compared to GLP-1–only drugs.
| Brand Name | Manufacturer | Route | FDA-Approved Use | FDA Approval Year |
|---|---|---|---|---|
| Mounjaro | Eli Lilly | Injectable (weekly) | Type 2 diabetes | 2022 |
| Zepbound | Eli Lilly | Injectable (weekly) | Chronic weight management | 2023 |
Important: This article is for educational purposes only and not intended as medical advice. Always work with a licensed healthcare provider before starting, stopping, or changing any medication.
Why Lab Tests Matter Before Starting Tirzepatide or Semaglutide
GLP-1 or GIP/GLP-1 Medications like semaglutide and tirzepatide work by changing how your body regulates blood sugar, appetite, and digestion. Labs help your provider:
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Identify underlying conditions that could affect treatment safety or effectiveness.
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Rule out contraindications such as certain endocrine disorders.
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Track baseline health data to measure future improvements (or spot side effects early).
Without this information, you risk starting a medication that isn’t the safest or most effective choice for your situation.
Common Lab Tests Used to Guide Medication Choice
1. A1C and Fasting Blood Glucose
Why it matters: Shows how well your body is managing blood sugar over time.
- Medication implications:
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Higher A1C may point toward a stronger need for blood sugar–lowering effects (both semaglutide and tirzepatide do this).
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If your blood sugar is already well-controlled, weight loss may be the primary goal — which can change dose considerations.
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2. Kidney Function (eGFR, Creatinine, BUN)
Why it matters: These medications are cleared through the kidneys. Poor kidney function can affect dosing or require avoiding certain drugs.
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Medication implications:
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Mild to moderate kidney issues may still allow use with careful monitoring.
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Severe kidney disease may require alternative treatments.
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3. Liver Function Tests (AST, ALT, ALP, Bilirubin)
Why it matters: The liver processes and metabolizes many drugs.
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Medication implications:
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Abnormal results may prompt closer monitoring or a different therapy.
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GLP-1 drugs have not been shown to cause liver injury in most patients, but caution is used if liver disease is present.
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4. Lipid Panel (Cholesterol, LDL, HDL, Triglycerides)
Why it matters: Weight loss medications can improve cholesterol profiles, but some patients need faster cardiovascular risk reduction.
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Medication implications:
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If cholesterol is high, tirzepatide’s strong metabolic benefits may be appealing.
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Semaglutide also reduces cardiovascular risk, which can be important for patients with heart disease.
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5. Thyroid Function (TSH, Free T4)
Why it matters: GLP-1 medications carry an FDA boxed warning for possible thyroid C-cell tumors in animal studies.
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Medication implications:
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If you have a history of medullary thyroid carcinoma or multiple endocrine neoplasia syndrome type 2, these drugs are not recommended.
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6. Amylase and Lipase
Why it matters: These enzymes are linked to pancreas health.
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Medication implications:
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High levels before treatment may require evaluation for pancreatitis risk before starting therapy.
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7. Vitamin & Nutrient Levels (Optional but Helpful)
Why it matters: Rapid weight loss can lead to deficiencies, especially in vitamin B12, vitamin D, and iron.
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Medication implications:
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Deficiencies should be corrected before or during treatment to avoid fatigue, weakness, and other side effects.
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How Providers Match the Right Drug to Your Profile
Once your lab tests for semaglutide or tirzepatide are back, your provider will look at:
| Factor | Semaglutide May Be Preferred | Tirzepatide May Be Preferred |
|---|---|---|
| Primary Goal | Cardiovascular protection + weight loss | Maximum weight loss + blood sugar control |
| A1C | Mild-to-moderate elevation | Higher A1C needing stronger glucose reduction |
| Side Effect Sensitivity | If you need slower dose escalation to reduce GI upset | If you tolerate GI side effects well and want faster results |
| Insurance Coverage | Covered for weight loss under Wegovy | Covered for weight loss under Zepbound (varies by plan) |
Realistic Expectations and Monitoring
Even after the “best match” medication is chosen, your provider will likely:
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Repeat labs every 3–6 months to monitor safety and progress.
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Adjust doses based on results and side effects.
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Combine medication with nutrition, exercise, and lifestyle support for best results.
Bottom Line
Lab work is not just a formality — it’s the foundation for choosing whether semaglutide, tirzepatide, or another drug is safest and most effective for you.
At Heally, our providers use comprehensive lab testing and telehealth visits to create a personalized plan. Whether you’re managing type 2 diabetes, looking to lose weight, or improving your overall metabolic health, we’ll help you find the safest and most effective path forward.
Heally can connect you to a knowledgeable doctor who can help you find the best way forward. You don’t have to navigate this alone; let’s find the right solution together, schedule your consultation with Heally today!
Sources
- New England Journal of Medicine: Once-Weekly Semaglutide in Adults with Overweight or Obesity
- PubMed: Tirzepatide Once Weekly for the Treatment of Obesity
- New England Journal of Medicine: Tirzepatide versus Semaglutide Once Weekly in Patients with Type 2 Diabetes
- Eli Lilly: News Release: Lilly’s tirzepatide shows additional 21.1% weight loss after 12 weeks of intensive lifestyle intervention, for a total mean weight loss of 26.6% from study entry over 84 weeks
- Diabetes Care: ADA Standards of Medical Care in Diabetes (2025)
- FDA Label: OZEMPIC (Semaglutide Injection) Medication Guide
- FDA Label: WEGOVY (Semaglutide Injection) Medication Guide
- FDA Label: RYBELSUS (Oral Semaglutide) Medication Guide
- FDA Label: MOUNJARO (Tirzepatide Injection) Medication Guide
- FDA Label: ZEPBOUND (Tirzepatide Injection) Medication Guide
Important Medical Information and Disclaimers
Medical Disclaimer
This article,“How Labs Determine if Semaglutide, Tirzepatide, or Another Drug is Right For You,” is for educational purposes only and is not intended to replace professional medical advice, diagnosis, or treatment. Always seek the advice of a qualified healthcare provider regarding any questions you may have about a medical condition, medication, or treatment plan. Never ignore professional medical advice or delay seeking it because of something you have read here.
GLP-1 receptor agonists such as semaglutide (marketed under brand names Ozempic®, Wegovy®, and Rybelsus®) and the dual GIP/GLP-1 agonist tirzepatide (marketed under brand names Mounjaro® and Zepbound®) are FDA-approved prescription medications for specific uses in type 2 diabetes management and, in some cases, chronic weight management. These medications are not over-the-counter supplements and should be used only under the guidance of a licensed healthcare provider.
Compounded Drug Warning
The FDA has not approved compounded drugs and has issued safety alerts about dosing errors, product contamination, and other quality concerns. Compounded drugs are custom formulations made by pharmacies and may vary in quality, safety, and effectiveness, which can increase the risk of side effects or treatment failure. The FDA has warned against using these versions due to issues with incorrect ingredients, poor storage, or improper dosage. Always get medications from a licensed pharmacy with a valid prescription.
Individual Results May Vary
Responses to GLP-1 therapy can vary from person to person. Factors such as diet, physical activity, sleep quality, underlying medical conditions, other medications, and individual metabolism can all influence both side effects and overall results. Clinical trial outcomes may differ from real-world experiences.
Possible Side Effects
Common side effects of GLP-1 medications may include:
- Nausea
- Vomiting
- Diarrhea
- Constipation
- Stomach pain or discomfort
- Decreased appetite
- Indigestion or gas
- Redness, itching, or soreness at the injection site
Most side effects are mild to moderate and may improve as your body adjusts to treatment. If you experience severe or persistent symptoms, contact your healthcare provider promptly.
Boxed Warning (Thyroid C-Cell Tumor Risk)
GLP-1 receptor agonists, including semaglutide, carry an FDA boxed warning regarding the potential risk of thyroid C-cell tumors. Do not use if you or a family member has a history of medullary thyroid carcinoma (MTC) or multiple endocrine neoplasia syndrome type 2 (MEN 2).
When to Seek Immediate Medical Attention
Contact your healthcare provider or seek emergency care if you experience:
- Severe abdominal pain that does not go away
- Signs of an allergic reaction (rash, swelling, difficulty breathing)
- Symptoms of pancreatitis (severe abdominal pain, vomiting)
- Symptoms of severe dehydration (dizziness, confusion, rapid heartbeat)
FDA Adverse Event Reporting
To report medication side effects to the FDA, visit www.fda.gov/medwatch or call 1-800-FDA-1088. You may also contact the medication’s manufacturer directly.
