MariTide: What It Is, What the Research Shows, and Is It Approved?

MariTide is one of the more scientifically interesting drugs in the obesity pipeline, because it does something backwards on purpose. Before getting to that, the headline: it is not approved by the FDA, and you cannot get it. Here's the honest picture.

What MariTide actually is

MariTide is an experimental medicine from Amgen, an American drug company. Its official generic name is maridebart cafraglutide, and its old lab code is AMG 133. You'll see all three names used for the same thing.

It's built differently from most drugs in this space. The Phase 2 paper calls it a peptide-antibody conjugate. Amgen calls it an antibody-peptide conjugate. Same thing, different word order. Let's take it apart:

• A peptide is a short chain of amino acids, the tiny building blocks that make up protein. Most weight-loss drugs you've heard of are peptides.
• An antibody is a large Y-shaped protein. Your immune system makes antibodies to tag germs, but drug companies can also design antibodies that latch onto one specific target in the body. Antibodies are much bigger than peptides, and they stay in your body far longer.
• A conjugate just means two parts joined together. In MariTide, an antibody is joined to two GLP-1-like peptides by short linkers.

Here's the key detail. The antibody is not just a carrier. According to the Phase 1 study, the antibody itself is the part that blocks the GIP receptor. The two attached peptides are the part that switches GLP-1 on. So one molecule does both jobs.

The antibody also makes the drug last. Peptides on their own get cleared from the body fairly quickly, which is why most of these drugs are taken weekly. In the Phase 1 study, MariTide's average half-life was about 21 days, and the researchers said this made injections every 4 weeks possible. Newer trials are testing whether people who have already lost weight can keep it off with injections every 8 or even every 12 weeks. None of those longer schedules has been proven yet. Our article on what MariTide trials are testing goes through each study.

The interesting part: it blocks GIP, and tirzepatide does the opposite

This is the bit worth slowing down for, because it's genuinely strange and most coverage skips it.

Your gut releases hormones after you eat. Two of them matter here:

• GLP-1: the 'I'm full' signal. It curbs appetite and slows how fast food leaves your stomach. This is what semaglutide (Ozempic, Wegovy) targets.
• GIP: another gut hormone released after meals. It's involved in insulin and in how your body handles fat.

Now here's the puzzle. An agonist switches a receptor on, like a key turning a lock. An antagonist blocks it, like jamming the lock so nothing else can turn it. Two drugs in serious development do opposite things to GIP:

Read that table again, because it shouldn't work. Tirzepatide turns GIP on and helps people lose weight. MariTide turns GIP off and also appears to help people lose weight. Those can't both be true for the obvious reason, so something more complicated is going on.

Scientists call this a paradox, and there's a whole review paper devoted to asking how two opposite approaches both ended up in serious drug development. The honest answer right now is that nobody fully knows. One leading idea is that constantly blocking a receptor and constantly stimulating it can end up in a similar place, because a receptor that's over-stimulated for long enough stops responding anyway. It's a bit like how you stop noticing a smell you've been sitting in. But that's a working theory, not a settled fact.

What it's studied for

• Obesity and weight loss: the main target, and the focus of the large ongoing trials
• Type 2 diabetes: a condition where blood sugar stays too high
• Obstructive sleep apnea, heart failure, and heart and blood vessel events: all in Phase 3 trials that have not finished or reported
• Raised liver fat: in a Phase 2b trial that has not reported

What the evidence really shows

Being precise here matters, because MariTide sits in an awkward middle spot. It's better evidenced than a pure research chemical, and much less evidenced than an approved medicine.

Published studies

• Phase 1 (published 2024, Nature Metabolism). An early safety study in 110 adults with obesity (NCT04478708). It tested single injections and a short run of three injections given every 4 weeks, against placebo. Weight loss increased with dose, and in the repeat-injection groups it lasted up to 150 days after the last injection. Early studies like this are small and short.
• Phase 2 (published 2025, New England Journal of Medicine). A 52-week trial in 592 people (NCT05669599), comparing MariTide with placebo, a dummy injection. Most groups got injections every 4 weeks, and one group got them every 8 weeks. In people without diabetes, average weight change ranged from -12.3% to -16.2% across MariTide groups, versus -2.5% on placebo. In people with type 2 diabetes it ranged from -8.4% to -12.3%, versus -1.7%.

Phase 2 is the middle stage of testing. It's real human evidence, but it's a smaller, shorter look designed largely to figure out what to test properly later.

Company-reported results, not yet published

• Phase 2, year two (maintenance). In February 2026, Amgen said most participants kept off the weight they had lost for another 52 weeks, on monthly or every-12-week injections, with very low rates of nausea and vomiting and no new safety signals. Amgen has not published the numbers behind this, so treat it as a company claim, not peer-reviewed evidence.
• Phase 2 in type 2 diabetes (NCT06660173). A 24-week trial in 409 adults with type 2 diabetes, against placebo. In February 2026, Amgen said monthly MariTide produced meaningful drops in blood sugar and weight. No journal paper has been published. As of 15 September 2026 the registry lists the trial as active but not recruiting.

Phase 3: running, none reported

Phase 3 is the big final stage: thousands of people, long follow-up, the evidence regulators actually decide on. Amgen's program is called MARITIME. By registry figures, its main trials include more than 20,000 people between them. None has reported results. Statuses below were checked on ClinicalTrials.gov on 15 September 2026.

Side effects

Side effects are not a footnote. In the Phase 2 trial, gut side effects (nausea, vomiting, that whole family) were common. The trial found they were less frequent when treatment started lower and was increased gradually. The researchers reported no unexpected safety signals, which is reassuring as far as it goes, but a 52-week Phase 2 trial is a small window in which to spot a rare problem.

Who talks about it, and why to be careful

MariTide gets attention for two reasons: the less-frequent-injection angle, and the fact that it's a credible challenger with a genuinely different mechanism. Both are legitimate reasons for scientists to be interested. Neither is a reason for you to buy anything. The gap between 'promising Phase 2 result' and 'medicine your doctor can prescribe' is exactly where a lot of drugs quietly fail, and it's also exactly where grey-market sellers make their money.

What this does not mean