What is MariTide?

A GLP-1 drug built the opposite way

Every GLP-1 drug on the market today is a small peptide, injected weekly, that activates the GLP-1 receptor. Tirzepatide adds a second peptide action on GIP. Retatrutide adds a third, on glucagon. MariTide, Amgen's obesity candidate, takes a different shape entirely. It is an antibody-peptide conjugate: a peptide that activates GLP-1, chemically attached to a monoclonal antibody fragment that blocks the GIP receptor rather than turning it on.

That is a real bet against the field's consensus. Tirzepatide and retatrutide both activate GIP because animal data suggested that helped weight loss. Amgen's own preclinical work pointed the other way, finding that chronic GIP receptor blockade produced comparable fat loss in their models. Nobody has run a trial that settles which theory is right. What exists so far is separate human data for each approach, and MariTide is the most advanced GIP-antagonist program in that argument.

The antibody half of the molecule is doing more than picking a target. Attaching a small peptide to a large antibody fragment slows how fast the kidneys clear it, stretching its half-life from days to weeks. That is the engineering trick behind the pitch that got Wall Street's attention: a shot every month, or even every quarter, instead of every week.

What the Phase 2 trial found

Amgen's Phase 2 data, published in the New England Journal of Medicine in 2025 and presented at the American Diabetes Association's annual meeting, split participants into two groups: adults with obesity or overweight without type 2 diabetes, and adults with obesity and type 2 diabetes.

In the non-diabetic group, the highest doses produced up to 20% mean weight loss at 52 weeks, with the weight-loss curve still trending down at the end of the study rather than flattening out. In the group with type 2 diabetes, weight loss ran lower, up to roughly 17%, alongside meaningful improvements in A1C. Both numbers put MariTide in the same general range as tirzepatide, though there has been no head-to-head trial and cross-trial comparisons are unreliable.

Wall Street's initial reaction to the full Phase 2 dataset was lukewarm. Some analysts had modeled higher numbers off the first 52-week readout, and the arms that matched those expectations came with a tolerability cost worth understanding before reading the results as an unambiguous win.

The dosing problem, and how Amgen is fixing it

The side effects are the same family every GLP-1 drug produces: nausea, vomiting, and constipation. What stood out in MariTide's Phase 2 data was how much those effects depended on how the dose was introduced. Arms that started participants at close to the full dose saw higher rates of vomiting and higher discontinuation. Arms that escalated the dose gradually over several months saw meaningfully fewer dropouts, with GI-related discontinuation in the dose-escalation arms under 8%.

Amgen carried that lesson directly into the Phase 3 program: every MARITIME trial uses a slow dose-escalation schedule. The company is also running a dedicated study, called MARITIME-Switch, enrolling around 300 people already on weekly Wegovy or Zepbound and moving them onto MariTide's every-8-week or every-12-week schedule, tracking weight change over 52 weeks. That trial exists to answer a narrower but commercially important question: does someone already stable on a weekly injection tolerate a bigger, less frequent dose as well as they tolerated the weekly one.

The Phase 3 MARITIME program

MariTide's late-stage program is four trials deep, each aimed at a different approval:

MARITIME-1 is the trial to watch first. It is powered to confirm the Phase 2 weight-loss signal at scale, over 72 weeks, and its primary readout is targeted for early 2027. Enrollment pace and any interim safety updates through the rest of 2026 will be the best signal of whether that timeline holds. A positive readout would put an FDA filing, and a realistic approval, no earlier than 2028.

How it stacks up against what is already available

MariTide has not been tested head-to-head against tirzepatide, semaglutide, or retatrutide, so any comparison has to lean on separate trials with different populations and durations. On that basis, MariTide's Phase 2 ceiling, 20% weight loss at 52 weeks, sits close to tirzepatide's published results and below retatrutide's 28.3% at 80 weeks. What MariTide is selling is not a higher ceiling on weight loss. It is dosing frequency: four to six injections a year instead of fifty-two, if the quarterly schedule holds up in Phase 3. Whether that convenience outweighs a possibly smaller effect size, for patients who could also just take a currently available weekly drug, is the commercial question Amgen is betting on.

What to do with this if you are shopping for a GLP-1 today

There is no legal path to MariTide outside of enrolling in one of the MARITIME trials. If you need treatment now, tirzepatide and semaglutide remain the FDA-approved options with the most real-world data behind them. See our semaglutide vs tirzepatide comparison for how those two stack up, or our GLP-1 program comparison for how to actually get access. Worth tracking over the next year: whether MARITIME-1 reproduces the Phase 2 weight-loss numbers, and whether Amgen's quarterly-dosing bet holds up against the tolerability trade-offs the earlier trial already surfaced.