Comparisons GLP-1 Medications vs Phentermine

GLP-1 Medications vs Phentermine

Side-by-side comparison of weight loss results, pricing, side effects, and clinical data.

GLP-1 Medications

~15-22%

Phentermine

~5-7%

Head-to-Head Comparison

Metric
GLP-1 MedicationsOzempic / Wegovy / Mounjaro / Zepbound
PhentermineAdipex-P / Lomaira
Drug Class
GLP-1 receptor agonists
Sympathomimetic amine (stimulant)
Administration
Weekly injection
Daily oral tablet
Dosing
Once weekly
Once daily
Avg. Weight Loss
~15-22%
~5-7%
Half-Life
5-7 days
~20 hours
Compounded Cost
$150-450/mo (compounded)
$10-30/mo (generic)
Brand Cost
$1,000-1,400/mo
$30-75/mo
FDA Approved
2021
1959
Key Trial
STEP and SURMOUNT programs
Various (5-7% weight loss over 12 weeks)

Side Effects Comparison

GLP-1 Medications

  • Nausea
  • Diarrhea
  • Vomiting

Phentermine

  • Increased heart rate
  • Insomnia
  • Dry mouth
  • Anxiety

Pros & Cons

GLP-1 Medications

Pros

  • +Dramatically more weight loss
  • +Metabolic benefits beyond weight
  • +Long-acting with weekly dosing

Cons

  • -Expensive
  • -Injectable
  • -GI side effects common

Phentermine

Pros

  • +Very affordable
  • +Oral tablet
  • +Fast-acting appetite suppression

Cons

  • -Limited to 12-week use
  • -Stimulant side effects
  • -Weight regain after stopping
  • -Not for patients with heart conditions

The Verdict

GLP-1 medications produce 2-4x more weight loss than phentermine with a completely different mechanism and safety profile. Phentermine is far cheaper ($10-30/mo vs $150-1,400/mo) but is limited to short-term use (12 weeks) and carries cardiovascular risks. GLP-1s represent a paradigm shift in obesity treatment.

STEP 9 compared semaglutide to phentermine-topiramate and showed comparable weight loss, though different side effect profiles.

Which Is Right for You?

Choose GLP-1 Medications if...

Patients seeking significant, sustained weight loss with metabolic benefits

Choose Phentermine if...

Patients needing short-term appetite suppression on a tight budget who have no cardiovascular risk

Frequently Asked Questions

Are GLP-1s better than phentermine?

For sustained weight loss, yes. GLP-1s produce significantly more weight loss (15-22% vs 5-7%), can be used long-term, and have metabolic benefits. Phentermine is limited to 12 weeks and carries stimulant risks.

Can I take phentermine and a GLP-1 together?

Some doctors prescribe them together, especially during the GLP-1 titration period. However, this is off-label and should only be done under medical supervision.

Why would anyone choose phentermine over GLP-1s?

Cost is the main reason — phentermine is $10-30/mo vs $150-1,400/mo for GLP-1s. It also works immediately and is a simple pill. Some patients use it as a bridge while waiting for GLP-1 access.

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