Key Takeaways
- Once-monthly injection — not weekly like all current approved GLP-1 drugs
- Bispecific antibody — structurally different from all other GLP-1 medications
- Activates GLP-1 receptors and blocks GIP receptors
- Phase 2: ~20% average weight loss over 52 weeks
- Phase 3 MARITIME trials are underway
- Possible FDA approval 2027–2028
What Makes MariTide Different
MariTide (AMG 133) is developed by Amgen. It is a bispecific antibody — the same drug category used in cancer immunotherapies — making it structurally unlike any other GLP-1 medication. Traditional GLP-1 drugs are peptides or small molecules. Bispecific antibodies are much larger proteins engineered to engage two targets simultaneously.
This different structure is part of what enables monthly dosing. Bispecific antibodies have much longer half-lives in the body than peptide GLP-1 drugs, which is why they don't need to be re-dosed weekly.
The GIP Blocking Mechanism
Every other drug in the pipeline either activates GIP (tirzepatide, retatrutide) or ignores it. MariTide blocks GIP — the opposite approach. Early research suggests that in some people, GIP signaling may blunt GLP-1's effectiveness. Blocking it may therefore enhance overall weight loss response.
| MariTide | Zepbound (Tirz) | Wegovy (Sema) | Retatrutide | |
|---|---|---|---|---|
| Drug type | Bispecific antibody | Peptide | Peptide | Peptide |
| GIP action | Blocks GIP | Activates GIP | No GIP effect | Activates GIP |
| Dosing | Monthly | Weekly | Weekly | Weekly |
| Avg weight loss | ~20% | ~20–22% | ~15% | ~24% |
| Status | Phase 3 | Approved | Approved | Phase 3 |
| Available now | No | Yes | Yes | No |
Phase 2 Results and Phase 3 Status
Amgen's Phase 2 data showed approximately 20% average body weight loss over 52 weeks with monthly dosing maintained throughout. Side effects were consistent with the GLP-1 drug class. Phase 3 MARITIME trials launched in 2024–2025.
| Milestone | Estimated Timing |
|---|---|
| Phase 3 MARITIME results | 2026–2027 |
| NDA submission | 2027 (estimated) |
| FDA review | 12 months |
| Earliest approval | 2027–2028 |
Compare MariTide with all pipeline drugs at the comparison hub, see the approval timeline, or return to the future GLP-1 hub.
Frequently Asked Questions
What is MariTide?
MariTide (AMG 133) is an investigational once-monthly weight loss injection from Amgen. It is a bispecific antibody that activates GLP-1 receptors and blocks GIP receptors — the opposite of tirzepatide's approach to GIP.
How much weight loss did MariTide show?
Phase 2 trials showed approximately 20% average body weight loss over 52 weeks with monthly dosing. Phase 3 MARITIME trials are currently underway.
Why does monthly dosing matter?
Long-term medication adherence is one of the biggest challenges in obesity treatment. Weekly injection fatigue is a real clinical problem. A monthly drug achieving comparable efficacy could produce better real-world outcomes simply by making it easier to stay on therapy.
How does MariTide differ from Zepbound?
Zepbound (tirzepatide) activates both GLP-1 and GIP receptors. MariTide activates GLP-1 but blocks GIP. Both achieved ~20% weight loss in trials. MariTide also requires monthly instead of weekly dosing.
When will MariTide be approved?
Phase 3 MARITIME trials are underway. Based on current timelines, FDA approval is possible in 2027–2028.
Monthly dosing is coming — weekly options work today.
While MariTide completes Phase 3, FDA-approved weekly GLP-1 medications achieve 20%+ weight loss through telehealth providers in most states.
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