What Are GLP-1 Medications? A Complete Guide to Semaglutide and Tirzepatide

Over the past several years, a class of medications called GLP-1 receptor agonists has moved from diabetes management to the forefront of obesity medicine. Two agents in particular — semaglutide and tirzepatide — have produced weight-loss results in clinical trials that were previously unachievable with medications alone.

If you've seen headlines about Ozempic, Wegovy, Mounjaro, or Zepbound — those are brand names for these same compounds. The terms are often used interchangeably in media coverage, which creates confusion about what these drugs actually are, how they differ, and who they're appropriate for.

This guide walks through the mechanism of action, the clinical evidence, common side effects, and the criteria physicians use to evaluate whether a patient may be a candidate.

What Is a GLP-1 Receptor Agonist?

GLP-1 stands for glucagon-like peptide-1 — a hormone naturally produced by the gut in response to eating. GLP-1 performs several jobs in the body:

• Stimulates insulin secretion in a glucose-dependent manner (helping manage blood sugar after meals)
• Suppresses glucagon (a hormone that raises blood sugar)
• Slows gastric emptying — food moves more slowly from the stomach to the intestine
• Acts on the brain's appetite centers to reduce hunger signals and increase satiety

GLP-1 receptor agonists are synthetic molecules that mimic or enhance these effects. The critical difference from the natural hormone: they have a much longer half-life, so their effects persist for days rather than minutes.

Semaglutide: Ozempic and Wegovy

Semaglutide is a GLP-1 receptor agonist developed by Novo Nordisk. It exists in two FDA-approved forms:

• Ozempic (semaglutide 0.5 mg, 1 mg, 2 mg) — FDA-approved for type 2 diabetes management. Frequently prescribed off-label for weight loss.
• Wegovy (semaglutide 2.4 mg) — FDA-approved specifically for chronic weight management in adults with obesity or overweight with at least one weight-related condition.

Both are administered as once-weekly subcutaneous injections, typically in the abdomen, thigh, or upper arm.

Clinical Evidence for Semaglutide

The STEP (Semaglutide Treatment Effect in People with obesity) clinical trial program enrolled thousands of participants across multiple studies. Key findings from STEP 1 — the largest trial in people without diabetes:

• Participants receiving semaglutide 2.4 mg lost an average of 14.9% of body weight at 68 weeks
• Placebo group lost an average of 2.4%
• 69% of semaglutide participants achieved ≥10% weight loss vs. 12% in placebo

These are results in the context of lifestyle intervention (reduced-calorie diet + increased physical activity) in both groups — the medication effect is the difference.

Tirzepatide: Mounjaro and Zepbound

Tirzepatide, developed by Eli Lilly, represents the next generation of this drug class. It is a dual GIP/GLP-1 receptor agonist — it activates both the GLP-1 receptor and the GIP (glucose-dependent insulinotropic polypeptide) receptor simultaneously.

• Mounjaro (tirzepatide) — FDA-approved for type 2 diabetes
• Zepbound (tirzepatide) — FDA-approved for chronic weight management

GIP is another gut hormone that complements GLP-1's effects. The dual-action mechanism appears to produce additive benefits on appetite regulation and metabolic function.

Clinical Evidence for Tirzepatide

The SURMOUNT clinical trial program demonstrated outcomes that exceeded previous weight-loss medications. From SURMOUNT-1:

• At the highest dose (15 mg), participants lost an average of 20.9% of body weight at 72 weeks
• Placebo group: 3.1%
• 57% of tirzepatide 15 mg participants achieved ≥20% weight loss

These figures approach the weight-loss outcomes typically seen with bariatric surgery — a meaningful threshold that was not previously achievable with pharmacotherapy alone.

Semaglutide vs. Tirzepatide: A Direct Comparison

When patients ask about the difference between these two medications, the honest answer is that both are highly effective — and the "better" choice depends on individual patient factors, insurance coverage, and physician judgment.

Factor	Semaglutide (Wegovy)	Tirzepatide (Zepbound)
Mechanism	GLP-1 receptor agonist	Dual GIP + GLP-1 receptor agonist
Average weight loss (trials)	~15% at 68 weeks	~20% at 72 weeks (highest dose)
Dosing	Once weekly injection	Once weekly injection
FDA approval (weight)	Wegovy approved 2021	Zepbound approved 2023
Cardiovascular data	SELECT trial: 20% reduction in CV events (SELECT trial, 2023)	SURPASS-CVOT ongoing; preliminary data positive
Common side effects	Nausea, vomiting, diarrhea, constipation	Similar GI profile; some studies show slightly higher nausea at initiation

A 2024 real-world observational study comparing the two found tirzepatide associated with greater weight loss at 12 months, but both groups showed clinically meaningful reductions. Head-to-head randomized trials are ongoing.

How These Medications Are Prescribed

Both semaglutide and tirzepatide require a prescription from a licensed physician. The prescribing process typically involves:

1. Medical history review — including current diagnoses, medications, and contraindications
2. BMI assessment — FDA indications are for adults with BMI ≥30, or BMI ≥27 with at least one weight-related condition (hypertension, type 2 diabetes, dyslipidemia, obstructive sleep apnea, cardiovascular disease)
3. Lab work consideration — physicians may evaluate kidney function, thyroid status, and metabolic panel
4. Dose titration plan — both medications start at low doses and increase gradually over weeks to months to reduce GI side effects
5. Ongoing monitoring — weight, side effects, and response are tracked through follow-up visits

Common Side Effects and How to Manage Them

The most frequently reported side effects are gastrointestinal, reflecting the medication's mechanism of slowing gastric emptying:

• Nausea — most common, especially during dose escalation; typically improves after several weeks
• Vomiting — less common than nausea; usually transient
• Diarrhea or constipation — can occur; staying hydrated and gradually increasing fiber intake helps
• Decreased appetite — intended effect; some patients experience it as discomfort early on
• Fatigue — reported by some patients, often during initiation

Physicians manage these effects through the titration schedule — starting at the lowest dose and holding at each level for 4 weeks before increasing. Most patients who tolerate the initial period find side effects diminish substantially as the body adjusts.

Less Common but Serious Considerations

Clinical trials and post-market surveillance have identified associations that physicians discuss with patients before prescribing:

• Pancreatitis — rare; patients with risk factors or symptoms (persistent severe abdominal pain) should contact their physician immediately
• Gallbladder disease — increased risk of gallstones associated with rapid weight loss generally; both medications carry a modest increased gallbladder event rate
• Diabetic retinopathy complications — observed in some diabetic patients on semaglutide; ophthalmologic monitoring may be recommended for high-risk patients
• Heart rate increase — both medications can cause a modest elevation in resting heart rate

What About Compounded Versions?

During periods of shortage, FDA-registered compounding pharmacies were authorized to produce compounded semaglutide and tirzepatide. As of 2025, FDA has declared shortages resolved for both branded products, which significantly limits the legal basis for compounded versions going forward.

Patients considering compounded GLP-1 medications should discuss the regulatory status, quality verification, and clinical considerations with their physician. Brand-name products from licensed manufacturers have undergone the full FDA approval process for safety, efficacy, and manufacturing quality.

Who May Be a Good Candidate?

FDA-approved indications provide a starting framework, but candidate evaluation is more nuanced in clinical practice. Physicians consider:

• BMI of 30 or higher (obesity), or BMI 27–29.9 with at least one weight-related comorbidity
• Prior weight-loss efforts through lifestyle interventions alone with insufficient results
• Absence of contraindications (thyroid cancer history, MEN2, pregnancy, severe GI disorders)
• Willingness to combine medication with dietary and lifestyle changes for optimal outcomes
• Ability to attend follow-up appointments for monitoring

The medication is not a standalone solution. Clinical trial participants in both the STEP and SURMOUNT programs received lifestyle counseling alongside the medication — and weight regain occurs when medication is discontinued without sustained behavioral changes.

The Telehealth Model for GLP-1 Treatment

Traditionally, access to obesity medicine specialists required referrals, long wait times, and in-person visits. Telehealth platforms have significantly expanded access — allowing patients to complete eligibility assessments, consult with physicians via video, and receive prescriptions managed through the telehealth encounter.

This model works well for motivated patients who are appropriate candidates and don't have complex comorbidities requiring specialist coordination. Physicians practicing in telehealth obesity medicine must be licensed in the patient's state of residence and follow the same prescribing standards as in-person practice.

PropPilot works with board-certified, licensed physicians trained in obesity medicine. All provider credentials are independently verified and publicly checkable through state medical boards and ABMS. Treatment requires a live video consultation — prescriptions are never issued without a face-to-face physician evaluation. Your health data is handled according to our Telehealth Consent and Privacy Policy.

Summary: Key Points to Remember

• GLP-1 medications work by mimicking gut hormones that regulate appetite, satiety, and blood sugar
• Semaglutide (Wegovy) and tirzepatide (Zepbound) are both FDA-approved for weight management; tirzepatide's dual mechanism appears to produce modestly greater average weight loss in trials
• Clinical trials show 15–21% average body weight reduction over 68–72 weeks — outcomes previously achievable only through surgery
• Both require once-weekly injection and a gradual dose titration to minimize GI side effects
• FDA indications: BMI ≥30, or BMI ≥27 with a weight-related comorbidity
• Contraindications include personal/family history of medullary thyroid carcinoma or MEN2
• Long-term use is typically required to maintain results; weight regain after discontinuation is common