What Are Incretins?
Incretins are hormones that your gut releases after you eat. Their job is to regulate blood sugar and signal to your brain that you've had enough food. The two main incretins are:
- GLP-1 (glucagon-like peptide-1) — suppresses appetite, slows digestion, increases insulin release
- GIP (glucose-dependent insulinotropic polypeptide) — enhances insulin response and influences fat metabolism
In people with obesity, these natural hormonal signals are often blunted or insufficient. GLP-1 medications restore and amplify these signals.
How GLP-1 Receptor Agonists Work
GLP-1 receptor agonists are lab-engineered molecules that mimic natural GLP-1 but last much longer in the body (natural GLP-1 breaks down within minutes). They work through several mechanisms:
- Slow gastric emptying — food stays in your stomach longer, so you feel full longer after meals
- Increase insulin secretion — but only when blood sugar is elevated, reducing hypoglycemia risk
- Reduce glucagon release — glucagon raises blood sugar, so suppressing it improves glucose control
- Signal satiety to the brain — GLP-1 receptors in the hypothalamus reduce hunger and food cravings
The combined effect is that patients naturally eat less, feel satisfied sooner, and lose weight without the constant willpower battle that characterizes most diets.
Types of Receptor Targeting
The field has evolved from single to multi-receptor targeting:
Single Agonist (GLP-1 only)
- Example: Semaglutide (Wegovy, Ozempic)
- Targets the GLP-1 receptor alone
- Produces ~15-17% weight loss
Dual Agonist (GLP-1 + GIP)
- Example: Tirzepatide (Zepbound, Mounjaro)
- Targets both GLP-1 and GIP receptors
- Produces ~20-23% weight loss
Triple Agonist (GLP-1 + GIP + Glucagon)
- Example: Retatrutide (in clinical trials)
- Adds glucagon receptor activation for increased energy expenditure
- Produces ~25-29% weight loss in trials
Medication Comparison
| Medication | Type | Route | Status | Typical Weight Loss | Manufacturer |
|---|---|---|---|---|---|
| Semaglutide (Wegovy) | GLP-1 | Weekly injection | FDA approved | ~15-17% | Novo Nordisk |
| Tirzepatide (Zepbound) | GLP-1/GIP | Weekly injection | FDA approved | ~20-23% | Eli Lilly |
| Orforglipron | GLP-1 (oral) | Daily tablet | NDA submitted | ~14.7% | Eli Lilly |
| Retatrutide | GLP-1/GIP/Glucagon | Weekly injection | Phase 3 | ~25-29% | Eli Lilly |
| Survodutide | GLP-1/Glucagon | Weekly injection | Phase 3 | ~18-19% | Boehringer Ingelheim |
| CagriSema | GLP-1 + Amylin | Weekly injection | Phase 3 | ~22-25% | Novo Nordisk |
Common Misconceptions
"It's just an appetite suppressant"
GLP-1 medications work through multiple hormonal pathways — appetite reduction is just one mechanism. They also improve insulin sensitivity, reduce systemic inflammation, and appear to have cardiovascular and kidney protective effects.
"It's a shortcut"
These medications correct an underlying hormonal imbalance. Obesity involves dysregulated hunger and satiety signaling, and GLP-1 medications address that biology directly, much like how blood pressure medication addresses hypertension.
"You'll lose all your muscle"
Any calorie deficit causes some lean mass loss. Studies show that GLP-1 medications produce a similar ratio of fat-to-muscle loss as dietary restriction alone. The key to preserving muscle is resistance training and adequate protein intake (at least 1.0-1.2 g per kg of body weight daily).
"The weight comes back when you stop"
Weight regain after discontinuation is common — studies show most patients regain a significant portion of lost weight within a year of stopping. This is why many experts now consider obesity a chronic condition requiring ongoing treatment, similar to managing high blood pressure or cholesterol.
The Role of Lifestyle
GLP-1 medications work best as part of a comprehensive approach:
- Protein-focused diet: Aim for at least 1.0-1.2 g of protein per kg of body weight daily to preserve lean muscle mass
- Resistance training: 2-3 sessions per week to maintain and build muscle during weight loss
- Cardiovascular exercise: 150+ minutes per week of moderate activity for overall health
- Sleep and stress management: Both significantly affect hormones that regulate weight
- Behavioral support: Building sustainable habits ensures long-term success
When to Talk to a Provider
You may be a good candidate for GLP-1 therapy if you have:
- A BMI of 30 or greater (obesity)
- A BMI of 27 or greater with at least one weight-related condition (high blood pressure, type 2 diabetes, high cholesterol, sleep apnea)
- Struggled to achieve or maintain weight loss through diet and exercise alone
A qualified provider can evaluate your full medical history and determine which medication, if any, is appropriate for you.