At a glance
| Field | Details |
|---|---|
| Brand names | Not yet approved (development code: AMG 133) |
| Targets | GLP-1R agonist + GIPR antagonist |
| Developer | Amgen |
| Modality | SC injection, once-monthly |
| Approval status | Phase 3 |
| Key efficacy | ~17.3% weight loss at 52 weeks (Phase 2) |
| Indications | Obesity |
User Sentiment
Monthly dosing is the headline in every patient discussion of MariTide. People on or tracking weekly GLP-1 drugs immediately respond to the idea of one injection per month — the math of 12 injections per year vs 52 is instantly legible. Phase 2 non-plateauing weight loss at 52 weeks is generating interest beyond just the convenience angle.
Example(What Phase 2 participants report)
AMG 133 trial participants noted weight loss that kept accumulating through the full 52-week period without the slowdown they'd experienced on weekly GLP-1 drugs at the 32–40 week mark. The monthly injection format was described as "like a background treatment" — easy to forget about between doses, no weekly injection routine to maintain.
How it works
Structurally unlike any other drug in this class. MariTide is a bispecific antibody-peptide conjugate: a monoclonal antibody that targets and blocks GIPR, with GLP-1R agonist peptides chemically attached to it. A single molecule that simultaneously activates GLP-1R and antagonizes GIPR.
This is mechanistically opposite to tirzepatide, which agonizes both GLP-1R and GIPR. MariTide is betting that blocking GIPR (rather than activating it) alongside GLP-1R agonism produces a useful weight loss profile — either recovering the original theory that GIP opposes weight loss, or demonstrating that GIPR antagonism in fat tissue has a distinct beneficial effect from GIPR agonism.
The antibody backbone provides the monthly dosing interval. Antibodies have long half-lives (~2–3 weeks for IgGs), which when combined with the attached peptides creates a drug that maintains therapeutic levels with once-monthly injection.
Intuition(GIPR antagonism vs agonism — the opposite bet)
Tirzepatide agonizes GIPR and gets 20.9% weight loss. MariTide antagonizes GIPR and gets ~17.3% weight loss. Both outperform semaglutide (~15%). This doesn't resolve which direction is "right" — it suggests that disrupting GIP signaling in either direction, combined with GLP-1R agonism, produces superior weight loss vs GLP-1 alone. The mechanisms are probably different: agonism may amplify the GLP-1 satiety signal via fat tissue and brain; antagonism may block GIP's glucose-dependent insulin secretion or appetite-opposing effects at higher doses. The biology is still being worked out.
Trial data
Phase 2 (52 weeks): ~17.3% weight loss with monthly injections. The notable feature: weight loss continued accumulating through the full 52-week period without the plateau that semaglutide typically shows around 40–52 weeks. If that non-plateauing trajectory holds in Phase 3, it implies a different long-term weight loss dynamic — potentially continuing past 52 weeks.
What to Expect
Month 1 — Single injection. GI side effects may lag slightly vs weekly drugs since peak drug concentration builds differently with monthly dosing.
Month 2–4 — Weight loss accumulating. Phase 2 trajectory shows continued loss without the plateau that weekly drugs often hit around month 6–9.
Month 6–12 — ~17.3% average at 52 weeks in Phase 2, with the curve still descending at that point. Total weight loss over full Phase 3 duration pending.
Not yet available — Phase 3 ongoing, FDA filing expected ~2027.
Dosing and administration
Once-monthly subcutaneous injection. Standard biologic storage — no special cold-chain requirements beyond refrigeration. Monthly cadence significantly reduces the patient touchpoint burden vs weekly drugs over a multi-year treatment course.
Development status
| Milestone | Status |
|---|---|
| Phase 2 | Complete — 17.3% at 52 weeks |
| Phase 3 | Enrolling |
| FDA filing | ~2027 estimated |
Safety profile
GI profile consistent with GLP-1 class in Phase 2. The GIPR antagonism is mechanistically distinct from tirzepatide's agonism — no unexpected safety signals attributable to the antibody format identified. Heart rate elevation similar to class. Full Phase 3 safety database pending.
Who It's For
- BMI ≥ 30 or ≥ 27 with weight-related conditions
- People who struggle with weekly injection routines — monthly format removes most of the adherence burden
- Patients who've plateaued on weekly GLP-1 drugs and want a mechanistically different option (GIPR antagonism vs agonism)
Monthly GLP-1 therapy changes the treatment experience fundamentally. If the weekly injection routine has been a barrier, MariTide is the most near-term alternative in Phase 3.
Summary(The MariTide picture)
Monthly dosing and GIPR antagonism — differentiated on two dimensions simultaneously from everything else in the class. Phase 2 non-plateauing weight loss trajectory at 52 weeks is the intriguing data point. Phase 3 will answer whether that trajectory continues and whether 17.3% at 52 weeks grows further at 72+ weeks.