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, 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. It's a peptide-antibody conjugate — which sounds intimidating, so 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 normally makes to tag germs. It's much bigger than a peptide, and it hangs around in your body far longer.
• A conjugate just means the two are stuck together. Amgen glued GLP-1 peptides onto an antibody.

Why bother? Because the antibody part acts like an anchor. Peptides on their own get cleared from the body fairly quickly, which is why most of these drugs are taken weekly. Bolting the peptide to an antibody makes it last much longer — long enough that MariTide is being tested on a monthly schedule instead. If that holds up, it would be a real practical difference for anyone who dislikes injections.

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 successful drugs 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 actually call this 'the GIP 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 blasting it can end up in a similar place, because a receptor that's over-stimulated for long enough stops responding anyway — 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 cardiovascular outcomes — all in trials that have not finished or 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.

What exists: one completed Phase 2 trial, published in the New England Journal of Medicine in 2025. 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. It enrolled 592 people over 52 weeks, and reported substantial average weight loss compared with placebo (a dummy injection), in people both with and without type 2 diabetes.

What doesn't exist yet: any finished Phase 3 result. Phase 3 is the big final stage — thousands of people, long follow-up, the evidence regulators actually decide on. Amgen is running a large Phase 3 program (called MARITIME), including trials in obesity, type 2 diabetes, sleep apnea, and heart failure. Some are enrolling tens of thousands of people between them. None have reported.

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 the dose was worked up gradually rather than started high. The researchers reported no unexpected safety surprises, 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 monthly-injection angle, and the fact that it's the most 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