If you're exploring weight loss medications, you've probably seen two very different options:
- GLP-1 agonists: Ozempic, Wegovy, Mounjaro, Zepbound
- Phentermine: An older stimulant-based appetite suppressant
They work differently, have different safety profiles, and produce different results.
Here's how to choose.
Quick Comparison
| GLP-1 Medications | Phentermine | |
|---|---|---|
| Drug class | Incretin mimetics | Stimulant |
| How it works | Mimics GLP-1 hormone | Suppresses appetite |
| Weight loss | 15-22% | 5-10% |
| FDA approval | Long-term use | Short-term use (weeks) |
| Administration | Injection (weekly) | Pill (daily) |
| Cost | $900-1,350/month | $15-50/month |
How They Work
GLP-1 Medications
GLP-1 agonists (semaglutide, tirzepatide) mimic a hormone your body naturally makes:
- Slow stomach emptying
- Signal fullness to your brain
- Reduce appetite
- Improve blood sugar control
They work with your body's natural systems.
Phentermine
Phentermine is a stimulant:
- Releases norepinephrine
- Reduces hunger signals
- Increases energy slightly
- Works like a mild amphetamine
It suppresses appetite by stimulating your system.
Weight Loss Results
GLP-1 Medications:
- Wegovy: ~15% average weight loss
- Zepbound: ~20-22% average weight loss
- Trials: 68-72 weeks
Phentermine:
- ~5-10% average weight loss
- Trials: 12-24 weeks (short-term studies only)
- Weight regain common after stopping
GLP-1s produce 2-4x more weight loss than phentermine.
Safety Differences
This is where GLP-1s have a major advantage.
GLP-1 Safety Profile
- FDA approved for long-term use
- Can take for years (studies go 2+ years)
- No cardiovascular risks (may actually help heart health)
- No dependency risk
Common side effects:
- Nausea
- Constipation/diarrhea
- Decreased appetite
Serious risks (rare):
- Pancreatitis
- Thyroid tumors (seen in rodents, not proven in humans)
- Gallbladder disease
Phentermine Safety Profile
- FDA approved for short-term use only (a few weeks)
- Not meant for chronic use
- Cardiovascular risks: increased heart rate, blood pressure
- Risk of dependency in some people
- Can't take if you have heart disease, uncontrolled hypertension, or history of drug abuse
Common side effects:
- Dry mouth
- Insomnia
- Constipation
- Increased heart rate
- Jitteriness
Who Should Use Each
GLP-1 Medications: Best For
- BMI 30+ (or 27+ with weight-related condition)
- Long-term weight management
- People with type 2 diabetes (some GLP-1s)
- Those who want sustainable results
- People who can afford/obtain GLP-1s
Phentermine: Best For
- Short-term jumpstart (under medical supervision)
- BMI 30+ who need quick initial loss
- People without cardiovascular risk factors
- Those who can't access GLP-1s
- Short-term use (weeks, not months)
Cost Comparison
GLP-1 Medications:
- List price: $900-1,350/month
- With insurance: $25-100/month (if covered)
- Savings cards available
Phentermine:
- Generic: $15-50/month
- Usually covered by insurance
- Widely available, no special authorization
Phentermine is much cheaper. But it's not approved for long-term use.
Can You Combine Them?
Some doctors prescribe phentermine with GLP-1 medications for a stronger effect. This is off-label and may increase side effects.
Potential issues:
- More nausea
- Higher heart rate
- More side effects overall
Products That Can Help
Exploring weight loss medications? These products may support your journey:
- Smart scale with body composition — Track weight loss progress beyond just the number
- Water bottle with time markers — Stay hydrated while on weight loss medication
- Food and symptom journal — Monitor how you feel on different medications
- Resistance bands set — Support muscle preservation during weight loss
Talk to your doctor about whether combination therapy makes sense for you.
What About Weight Regain?
GLP-1s: Weight regain happens if you stop, but studies show maintenance at lower doses is possible. Many people need to stay on GLP-1s long-term.
Phentermine: Weight regain is very common after stopping. Because it's only approved for short-term use, you're expected to stop eventually.
Bottom Line
GLP-1 medications are more effective and safer for long-term use. If you can access and afford them, they're the better choice for most people.
Phentermine remains an option for short-term use when GLP-1s aren't available or affordable. It's cheaper but less effective and not safe for chronic use.
The best medication depends on your health history, insurance coverage, and treatment goals.
Work with your healthcare provider to determine which medication is appropriate for you. This is general information, not medical advice.
