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Comparison

Retatrutide vs Tirzepatide

Retatrutide vs Tirzepatide: head-to-head on weight-loss potential, mechanism, side effect profile, and current availability.

003
Retatrutide
Fat LossEvidence: Moderate

Retatrutide is the newest weight-loss compound in development at Eli Lilly. It's a stronger cousin of Tirzepatide (Mounjaro / Zepbound) and pulls bigger weight loss in trials, often 20%+ of body weight. One injection per week. Side effects are real, especially in the first few weeks.

Onset
80
Documentation
95
Side intensity
100
Popularity
90
008
Tirzepatide
Fat LossEvidence: Strong

Tirzepatide is the prescription weight-loss drug sold as Mounjaro (diabetes) or Zepbound (weight loss). It hits two appetite-control receptors at once. Most users lose 15-20% of body weight over several months. One injection per week.

Onset
80
Documentation
95
Side intensity
100
Popularity
95
Side-by-side
Field
Left
Right
Category
Fat Loss
Fat Loss
Half-life
~6 days
~5 days
Route
Subcutaneous
Subcutaneous
Schedule
Once weekly
Once weekly
Cycle length
Open-ended, titrate over 4-6 months
Open-ended, titrate over months
Dose
Start 2mg sub-q weekly. Titrate by 2mg every 4 weeks based on tolerance. Trials went up to 12mg; most users plateau benefit at 8-12mg.
Start 2.5mg weekly. Titrate by 2.5mg every 4 weeks. Common max 10-15mg.
FDA
Investigational. In Phase 3 trials with Eli Lilly. Not yet approved.
Approved as Mounjaro (2022, type 2 diabetes) and Zepbound (2023, obesity).
WADA
Banned (S2)
Not listed
Natty?
Not natty
Not natty
Prescribed
Not yet available by prescription. Trial-only access through Lilly's clinical program.
Yes — widely prescribed by primary care, endocrinologists, and obesity-medicine specialists.
Top side effects
Nausea (especially first 2 weeks of each titration step); Constipation or diarrhea; Fatigue / lethargy
Nausea; Constipation; Reflux

Which one should you pick?

Pick Retatrutide if people plateaued on tirzepatide or users targeting >15% body weight loss.

Pick Tirzepatide if users who couldn't tolerate semaglutide or metabolic-syndrome adults under provider guidance.