Retatrutide vs semaglutide: how do they compare?

Core Comparison

Retatrutide

• Triple receptor agonist (GLP-1 + GIP + glucagon)
• Weekly subcutaneous injection
• 24.2% mean weight loss at 12 mg in the 2023 Phase 2 obesity trial over 48 weeks
• 28.3% weight loss at 12 mg in TRIUMPH-1 over 80 weeks using the efficacy estimand
• Not FDA-approved; Lilly plans BLA submission in Q1 2027

Semaglutide

• Single receptor agonist (GLP-1 only)
• Weekly subcutaneous injection (Wegovy, Ozempic)
• 14.9% mean weight loss at 2.4 mg (STEP 1, 68 weeks)
• FDA-approved since 2021 for obesity (Wegovy)

Mechanism Differences

Semaglutide (GLP-1 only)

• Appetite suppression
• Delayed gastric emptying
• Insulin sensitization
• Modest cardiovascular effects

Retatrutide (GLP-1 + GIP + glucagon)

• All of the above from GLP-1 activity
• Additional GIP: further appetite effects, metabolic enhancement
• Additional glucagon: increased hepatic lipolysis, energy expenditure
• "Burn" component not present in semaglutide

The glucagon receptor is the key differentiator. It increases basal metabolic rate through enhanced fat utilization — effectively helping patients burn more calories, not just eat less.

Weight Loss Comparison in Context

Cross-trial context:

• Semaglutide 2.4 mg (STEP 1, ~48 weeks interpolated): ~12%
• Retatrutide 12 mg (Phase 2 obesity trial, 48 weeks): 24.2%
• Retatrutide 12 mg (TRIUMPH-1 Phase 3, 80 weeks, efficacy estimand): 28.3%

The 24.2% figure is from the Phase 2 obesity trial, not TRIUMPH-1. These are not head-to-head data.

Side Effect Comparison

GI effects

• Semaglutide: nausea 44%, diarrhea 30%, vomiting 24%
• Retatrutide: nausea 45%, diarrhea 30%, vomiting 18%

Similar GI burden rates, though patient reports suggest retatrutide's effects may be more intense when they occur.

Heart rate

• Semaglutide: 4–6 bpm increase
• Retatrutide: 5–10 bpm increase

Other effects

• Both: injection site reactions, fatigue, headaches
• Retatrutide: slightly more hair loss
• Both: theoretical thyroid and pancreatic concerns from class warning

FDA Status and Availability

Semaglutide

• FDA-approved as Wegovy (obesity), Ozempic (diabetes), Rybelsus (oral)
• Cardiovascular indication approved (SELECT trial)
• Widely available at pharmacies
• Insurance coverage has expanded significantly

Retatrutide

• Not FDA-approved
• Lilly-planned BLA submission: Q1 2027
• FDA review would occur after submission; approval timing is not guaranteed
• Will be subject to typical 1-year insurance coverage lag post-approval
• No compounded availability expected (new drug, different regulatory path)

Cost Comparison

Semaglutide

• Brand Wegovy list: ~$1,350/month
• Direct cash program: ~$499/month
• With insurance: varies; often $25–$100 copay
• Compounded: $150–$400/month

Retatrutide (projected)

• Brand expected price: similar to Zepbound (~$1,000–$1,200/month list)
• Direct cash program: likely ~$399–$599/month
• Compounded: initially not available; may become available in shortage scenarios

Who Benefits More From Retatrutide

• BMI > 35 with significant weight loss goal
• Previous inadequate response to semaglutide
• Younger patients with minimal cardiovascular disease
• Those prioritizing maximum weight loss efficacy
• Patients with visceral fat concerns (glucagon receptor effect)

Who Benefits More From Semaglutide

• Modest weight loss goals (BMI 27–32)
• Cardiovascular disease or significant risk factors (CV indication)
• Those who want longer safety track record
• Cost-constrained patients (cheaper cash path)
• Those who tolerated semaglutide well
• Insurance covers semaglutide but not retatrutide

Switching Scenarios

Semaglutide → Retatrutide

• Common scenario for semaglutide non-responders or plateau patients
• Start retatrutide at 2 mg (standard starting dose)
• Titrate normally regardless of previous semaglutide dose
• Expect 1–2 weeks of GI adjustment as glucagon/GIP mechanisms kick in

Retatrutide → Semaglutide

• Typically driven by cost, access, or side effect tolerability
• Start semaglutide at 0.25 mg and titrate normally
• Expect some regain during the switch window

Cannot Combine

Both drugs activate GLP-1 receptors. Stacking them:

• Provides no additional benefit (receptors saturate)
• Substantially increases side effects
• Increases cost without benefit
• Is not clinically indicated under any circumstance

Pregnancy and Fertility

Both are:

• Not recommended during pregnancy
• Should be stopped 8 weeks before attempted conception
• Similar safety profile in pregnancy (both limited data)

Long-Term Use

Semaglutide

• Available data up to 2–3 years in trials
• Real-world experience since 2021
• Long-term safety established

Retatrutide

• Available data up to 48–72 weeks
• Long-term data accumulating post-approval
• Some uncertainty about 2+ year effects

Decision Framework

Choose semaglutide if:

• BMI 27–32 with moderate weight loss goal
• CV disease or strong CV risk factors
• Have insurance coverage
• Want established safety track record
• Budget is the main constraint

Choose retatrutide if:

• BMI > 35 and significant weight loss goal
• Previous semaglutide inadequate response
• Priority is maximum efficacy
• Can tolerate GI effects
• Cost/access acceptable

Bottom Line

Retatrutide produces substantially more weight loss than semaglutide. Semaglutide has longer track record, broader access, and cardiovascular indication. For patients with significant weight loss goals who can tolerate GI side effects, retatrutide becomes preferred once available. For modest goals or CV-indicated patients, semaglutide remains a reasonable first choice.

See the retatrutide guide. Related: vs tirzepatide, trial results.