Orforglipron vs Tirzepatide: Lilly's Pill vs Lilly's Injection
Both come from Eli Lilly. Tirzepatide (Mounjaro, Zepbound) is a weekly GLP-1 and GIP injection that took off 20.9% of body weight at 72 weeks. Orforglipron (Foundayo) is a daily GLP-1 pill that took off 11.2% over the same length of trial. Tirzepatide roughly doubles the weight loss; orforglipron is a pill and works as maintenance after tirzepatide.
Overview
Tirzepatide is a weekly peptide injection that activates both the GIP and GLP-1 receptors. It produced the largest weight loss of any approved drug in SURMOUNT-1 (20.9% at 15mg over 72 weeks) and is registered in Australia as Mounjaro.
Orforglipron is a daily small-molecule tablet that activates only the GLP-1 receptor. ATTAIN-1 ran for the same 72 weeks and the top dose averaged 11.2%. The FDA approved it as Foundayo in April 2026; it is under TGA evaluation in Australia.
Lilly positions the two as partners rather than rivals: tirzepatide to lose the weight, orforglipron to keep it off without needles.
Side-by-Side Comparison
| Attribute | Orforglipron (Foundayo) | Tirzepatide |
|---|---|---|
| Receptors | GLP-1 | GIP + GLP-1 |
| Form | Daily tablet | Weekly injection |
| Weight loss, 72 weeks | 11.2% | 20.9% (15mg) |
| Lean share of weight lost | 26.9% | About 25% |
| Resting heart rate rise | +4 to 9 bpm | About +2 bpm |
| Role after the other | Kept 74.7% of tirzepatide weight loss at 1 year | Not studied as maintenance after orforglipron |
| Main interaction | CYP3A4 inhibitors and inducers | Oral contraceptives (delayed gastric emptying) |
| Australia (Nov 2026) | Under TGA evaluation | Registered (Mounjaro) |
Key Differences
Receptors:
- Orforglipron: GLP-1 only, partial agonist
- Tirzepatide: GIP and GLP-1 dual agonist
Weight loss over 72 weeks (separate trials):
- Orforglipron 17.2mg: 11.2% (ATTAIN-1)
- Tirzepatide 15mg: 20.9% (SURMOUNT-1); 5mg gave 15.0%, already more than top-dose orforglipron
Maintenance after tirzepatide (ATTAIN-MAINTAIN):
- People switched from tirzepatide to orforglipron kept 74.7% of their weight loss at one year, versus 49.2% on placebo
- No arm stayed on tirzepatide, so it does not prove equivalence
Lean mass share of weight lost:
- Orforglipron: 26.9% (DXA subgroup)
- Tirzepatide: about 25% (SURMOUNT-1 DXA). Both match dieting alone
- Absolute lean loss is higher on tirzepatide because total weight loss is higher
Heart rate:
- Orforglipron: +4 to 5 bpm on label, up to about 9 bpm at the top trial dose in a 2026 meta-analysis
- Tirzepatide: about +2 bpm in the same meta-analysis, among the lowest in the class
Practicalities:
- Orforglipron: daily tablet, CYP3A4 interactions (9mg cap with strong inhibitors, simvastatin 20mg cap)
- Tirzepatide: weekly injection, cold-chain pens or vials, reduces oral contraceptive absorption after starting and dose steps
When to Use Which
Choose tirzepatide if:
- You want the most weight loss from an approved drug
- You are in Australia and want something registered now
- You are stacking chronotropic compounds and want the smaller heart rate rise
- Weekly injections do not bother you
Choose orforglipron if:
- You have reached your goal on tirzepatide and want an oral maintenance option
- You cannot or will not inject
- You only need modest weight loss (around 10%)
Monitoring for both: liver enzymes, lipase, creatinine and eGFR (cystatin C if muscular), lipids, HbA1c, and a resting heart rate log.
Clinical Context
Tirzepatide is the stronger drug by a wide margin and has a lower heart rate signal. Orforglipron's niche is oral maintenance and patients who will not inject. ATTAIN-MAINTAIN supports switching after tirzepatide, with about three quarters of the weight loss kept at one year, but it did not compare against staying on tirzepatide. Both carry the class warnings: pancreatitis, gallbladder disease, dehydration-related kidney injury and the thyroid C-cell boxed warning.
Bodybuilder Context
For a cut, tirzepatide gives more fat loss per week and a smaller heart rate rise, which matters if clenbuterol, T3 or trenbolone are in the stack. Lean mass share is similar on both, so muscle retention comes down to training and protein, not the drug. Orforglipron makes sense as a post-cut maintenance tool to hold appetite down without weekly pins. In Australia, tirzepatide is the one you can get legally today; grey-market orforglipron is an unverified small molecule.
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