Weight & Metabolic
MariTide (maridebart cafraglutide)
aka MariTide · maritide · maridebart cafraglutide · maridebart · AMG 133 · AMG133 · AMG-133 · amgen monthly jab · amgen weight loss jab · monthly jab · monthly weight loss jab · mari tide · maritid · maratide · maridebart cafraglutid
Grade
Amgen's experimental once-a-month weight-loss injection. It is an antibody with two GLP-1 peptides attached, not a peptide, and it is still in Phase 3 trials, so it is not an approved medicine anywhere.
- Class
- Antibody-peptide conjugate: a fully human monoclonal antibody that blocks the GIP receptor, chemically linked to two GLP-1 analogue peptides. Not a peptide on its own; a large protein biologic given by monthly injection
- Evidence
- Grade B · Promising human evidence
- Sport / WADA
- Prohibited at all times under S0 (non-approved substances). The WADA 2026 Prohibited List bans any pharmacological substance not covered elsewhere on the List and with no current approval by any governmental regulatory health authority for human therapeutic use, explicitly including drugs under clinical development.
- Last reviewed
- 2026-10
Grade B · Promising human evidence
Why this grade
Real, published, placebo-controlled human trials, but no Phase 3 results yet. The main evidence is one 52-week Phase 2 trial in 592 adults (NEJM 2025): in people with obesity, average weight loss was 12.3% to 16.2% versus 2.5% on placebo, counting everyone who started (treatment-policy estimand); Amgen's headline figure of up to about 20% counts only people who stayed on treatment. A Phase 1 study (Nature Metabolism 2024) also showed dose-dependent weight loss. All trials were run by the manufacturer, Amgen. The large Phase 3 MARITIME trials are under way and have not reported. No regulator has approved it.
What is it?
Why people buy it
People are interested in it to lose weight. It is a new injection you would take once a month, not once a week.
What we actually know
- •It is not a peptide. It is an antibody (a large protein) with two small hormone pieces attached.
- •One study followed 592 people for a year. People with obesity lost about 12 to 16% of their weight.
- •People on a dummy treatment lost about 2 to 3%. The company also quotes about 20%, counting only people who kept taking it.
- •It is still being tested in large studies. It is not a licensed medicine in the UK or anywhere else.
What might happen
- •Weight loss looks likely, going by that one study. The bigger studies have not finished.
- •Feeling sick and being sick were common, mostly after the first dose. Starting on a lower dose helped.
- •Some people stopped taking it because of side effects.
- •Long-term safety is unknown.
- •The real drug is made in living cells. A vial sold online under this name is very unlikely to be it.
- •It is banned in sport at all times, because it is not an approved medicine.
Bottom line
Promising results in people from one good-sized study, but it is not finished testing. Nothing sold online is the real product.
Know someone taking this?
Send on WhatsAppMost GLP-1 jabs are like topping up a car every week. MariTide is like fitting a much bigger fuel tank, so you fill up once a month. The test drives so far look good, but the long road test (Phase 3) is still going, and nobody sells the real car at the roadside.
How is it meant to work?
A dual-action biologic. Its two GLP-1 peptide arms activate GLP-1 receptors, reducing appetite, slowing gastric emptying and improving glucose-dependent insulin release, as other GLP-1 medicines do. Its antibody backbone blocks the GIP receptor; this is the opposite approach to tirzepatide, which activates GIP receptors. The combined molecule reduced body weight in mice and monkeys before human trials. The antibody gives it a very long duration of action, supporting monthly or less frequent subcutaneous injection in trials.
What's it studied for?
Research contexts. Not proven uses, and not recommendations.
Does the human evidence stack up?
Promising, from one substantial published trial. The Phase 2 trial (NEJM 2025, n=592) showed 12.3% to 16.2% average weight loss at 52 weeks versus 2.5% on placebo in people with obesity, and 8.4% to 12.3% versus 1.7% in people with type 2 diabetes, counting everyone who started. A Phase 1 study (Nature Metabolism 2024) showed dose-dependent weight loss lasting months after the last dose. Gastrointestinal side effects were common, especially after the first dose. All trials were funded by Amgen, and the Phase 3 MARITIME trials have not reported. There are no long-term safety data.
What could go wrong?
- !Not licensed by the MHRA or any other regulator. Its benefit-risk balance has not been signed off for any use
- !Nausea and vomiting were common in the Phase 2 trial, mainly after the first dose; about 11% stopped for side effects in the dose-escalation arms (Amgen figure)
- !Evidence rests on one Phase 2 trial and Phase 1 studies, all run by the manufacturer; Phase 3 results are not yet available
- !Amgen's headline 'up to about 20%' weight loss counts only people who stayed on treatment; counting everyone who started, the obesity-cohort range was 12.3% to 16.2%
- !Bone mineral density: analysts raised a Phase 1 signal at the highest dose in 2024. Amgen says it sees no association, but this has not yet been settled by Phase 3 data
- !Very long-acting: if side effects occur, the drug cannot be quickly stopped and cleared
- !GREY MARKET: the real drug is a large antibody made in living cells. Anything sold online as 'MariTide' or 'AMG 133' is unlicensed and is very unlikely to be the trial product
Is it legal in the UK?
Investigational drug, not a licensed UK medicine. The MHRA has not granted a marketing authorisation, and it is not available on prescription or the NHS. Legitimate access is only through a registered clinical trial. Anything sold to UK buyers under the name 'MariTide' or 'AMG 133' is an unlicensed product of unknown content; supplying it for human use would breach the Human Medicines Regulations 2012.
Key trials
- NCT05669599· Phase 2· Completed
Dose-ranging study of AMG 133 in adults with overweight or obesity, with or without type 2 diabetes
592 participants, 52 weeks; published in NEJM 2025.
- NCT06858839· Phase 3· Active, not recruiting
MARITIME-1: Maridebart cafraglutide in obesity or overweight without type 2 diabetes
About 3,850 participants; started March 2025.
- NCT06858878· Phase 3· Active, not recruiting
MARITIME-2: Maridebart cafraglutide in obesity or overweight with type 2 diabetes
About 1,100 participants; started March 2025.
- NCT07037433· Phase 3· Recruiting
MARITIME-CV: Cardiovascular outcomes with maridebart cafraglutide
About 12,800 participants planned.
Sources
- 01Once-Monthly Maridebart Cafraglutide for the Treatment of Obesity - A Phase 2 Trial — Jastreboff AM, et al., New England Journal of Medicine (2025)
n=592; 52 weeks; -12.3% to -16.2% vs -2.5% placebo (obesity cohort, treatment-policy estimand); -8.4% to -12.3% vs -1.7% with type 2 diabetes.
- 02A GIPR antagonist conjugated to GLP-1 analogues promotes weight loss with improved metabolic parameters in preclinical and phase 1 settings — Véniant MM, et al., Nature Metabolism (2024)
Structure (antibody plus two GLP-1 peptides), mouse and monkey data, and Phase 1 results in people with obesity.
- 03Amgen announces robust weight loss with MariTide in people living with obesity or overweight at 52 weeks in a Phase 2 study, Amgen press release (2024)
Company figures: up to about 20% (efficacy estimand); about 11% discontinued for any adverse event in dose-escalation arms; no association with bone mineral density changes.
- 04Amgen provides statement on MariTide Phase 1 data, Amgen company statement (2024)
Response to questions about Phase 1 bone mineral density data: Amgen says it does not see an association.
- 05Evaluation of Maridebart Cafraglutide in Adult Participants Without Type 2 Diabetes Mellitus Who Have Obesity or Overweight (MARITIME-1), ClinicalTrials.gov (2025)
Phase 3; about 3,850 participants; active, not recruiting.
- 06World Anti-Doping Code International Standard: Prohibited List 2026, World Anti-Doping Agency (2026)
S0 non-approved substances: drugs under clinical development are prohibited at all times.
Related
Before you trust a vial
Peptides are freeze-dried for a reason. If you have seen MariTide (maridebart cafraglutide) sold pre-mixed in a ready-to-use pen or syringe, here is why that is a red flag for potency, sterility and dosing.
Storage & stability →Stay posted
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