What is MariTide?
MariTide (maridebart cafraglutide, formerly AMG 133) is Amgen's entry into the obesity drug market. It's a first-in-class antibody-peptide conjugate that combines two mechanisms in a single molecule: it activates the GLP-1 receptor (like Wegovy and Ozempic) while simultaneously blocking the GIP receptor.
This is a fundamentally different approach from tirzepatide (Zepbound/Mounjaro), which activates both GLP-1 and GIP receptors. MariTide bets that blocking GIP while activating GLP-1 produces better outcomes than dual activation.
The other major differentiator: MariTide is dosed once per month, compared to weekly injections for semaglutide and tirzepatide.
How does it work?
MariTide uses an antibody-peptide conjugate (APC) platform. In simple terms:
- A GLP-1-mimicking peptide (the drug) is chemically attached
to an anti-GIP antibody (the carrier).
- The antibody portion blocks GIP receptors, preventing GIP
signaling.
- The peptide portion activates GLP-1 receptors, providing
the standard GLP-1 effects (appetite suppression, blood sugar control, slowed gastric emptying).
- The antibody carrier gives MariTide a very long half-life,
enabling once-monthly dosing.
The GIP-blocking hypothesis is controversial in the field. Tirzepatide's success came from GIP activation, and some researchers believe dual agonism is the optimal approach. Amgen's position is that GIP receptor signaling can promote fat storage, and blocking it may enhance fat loss beyond what GLP-1 agonism alone achieves.
Clinical trial results
MariTide is in Phase 2 and Phase 3 trials as of early 2026.
Phase 2 data (presented 2024): Participants lost up to approximately 14.5% of body weight at 12 weeks on the highest dose. Notably, this was only 12 weeks of treatment — a short duration by GLP-1 trial standards. Extrapolating from 12-week data is speculative, but the rate of loss was competitive with or faster than semaglutide and tirzepatide at comparable timepoints.
Weight maintenance signal. Perhaps the most interesting finding: some participants who stopped MariTide appeared to maintain their weight loss better than is typical for GLP-1 discontinuation. The extended pharmacological effect (the drug stays active in the body for weeks after the last dose due to the antibody carrier) may provide a natural buffer against immediate regain.
Phase 3 (MARITIME program): Multiple Phase 3 trials are enrolling as of 2026, including head-to-head studies against placebo and against existing treatments. Results are expected in 2027.
The monthly dosing advantage
Once-monthly injection is a significant practical advantage:
Adherence. Fewer injections means fewer opportunities for missed doses. Weekly injection adherence rates drop over time; monthly injections may be easier to maintain long-term.
Lifestyle. One injection per month versus four creates meaningfully less treatment burden. This matters especially for patients who dislike injections or have needle anxiety.
Side effect management. GLP-1 GI side effects (nausea, vomiting, constipation) typically spike after each injection. Monthly dosing means fewer spikes, though the sustained drug level could theoretically mean more persistent lower-grade side effects. Real-world data will clarify this.
Side effects
The Phase 2 side effect profile was broadly consistent with other GLP-1 receptor agonists:
- Nausea (most common, though potentially less episodic
than weekly injections)
- Vomiting
- Diarrhea
- Injection site reactions (expected given the larger
injection volume for an antibody-peptide conjugate)
Discontinuation rates for side effects were in the 10–15% range, comparable to semaglutide trials.
When could it be available?
Based on current timelines:
Optimistic: Phase 3 data readout in late 2027, FDA submission in 2028, potential approval in late 2028 or 2029.
Realistic: Approval in 2029–2030. Amgen is a large pharma company with deep regulatory experience, but the novel mechanism (GIP blockade vs. agonism) may attract additional FDA scrutiny.
What this means for patients
MariTide represents three things for the market:
Competition. A credible third player (alongside Novo Nordisk and Eli Lilly) entering the obesity drug space should drive pricing competition over time.
Convenience. Monthly dosing is a genuine quality-of-life improvement for patients who plan to be on long-term therapy.
Science. The GIP-blocking vs. GIP-activating debate will have real clinical data to resolve it. If MariTide performs comparably to tirzepatide, it validates an entirely new approach to obesity pharmacotherapy.
MariTide isn't an option today, but it's worth watching. For the full landscape of drugs in development, see our GLP-1 pipeline tracker.