Monthly Weight-Loss Injections? What MariTide Trials Are Testing

A weight-loss injection once a month, or even four times a year, sounds like a big change from the weekly shots people know today. MariTide is the drug behind most of that talk. This article looks at what the trials are really testing, and what has actually been shown so far.

What MariTide is, in plain language

MariTide is the name Amgen uses for maridebart cafraglutide, its experimental obesity drug. Its old lab code is AMG 133. All three names mean the same molecule. For the background on how it works, see our MariTide profile.

Amgen describes it as an antibody-peptide conjugate that switches on the GLP-1 receptor and blocks the GIP receptor. The published Phase 2 paper uses the mirror wording, a peptide-antibody conjugate. The Phase 1 paper explains the build: an antibody that blocks the GIP receptor, joined to two GLP-1-like peptides by short linkers.

• GLP-1 is a gut hormone signal linked to fullness. Drugs like semaglutide switch it on. Our GLP-1 explainer covers the basics.
• GIP is another gut hormone signal. Tirzepatide switches it on. MariTide does the opposite and blocks it.
• The antibody part matters for timing. Antibodies stay in the body far longer than small peptides. In the Phase 1 study, the average half-life was about 21 days, which the authors said made every-4-week dosing possible.

Current status, checked September 15, 2026: MariTide is investigational. It is not in the FDA's Drugs@FDA database, and Amgen's own August 4, 2026 results release still lists its obesity studies as ongoing Phase 3 trials. It is not a medicine you can be prescribed.

Starting treatment vs keeping weight off

Trials ask two different questions, and they are easy to mix up.

• Starting treatment. People begin the drug and researchers measure how much weight they lose compared with placebo, a dummy injection. The Phase 2 trial and the main MARITIME-1 and MARITIME-2 Phase 3 trials are built this way.
• Maintaining a result. People have already lost weight, either on MariTide or on another drug. Researchers then test whether a lighter schedule, such as fewer injections, keeps the weight off. The extension trials and the MARITIME-SWITCH trial are built this way.

Most of the talk about injections every 8 or 12 weeks is about the second question. A schedule that holds weight steady after loss is not the same as a schedule that causes the loss in the first place. The trials treat them separately, so this article does too.

The trials, side by side

This table covers every MariTide study where the injection schedule is part of the question, plus the main Phase 3 trials. It lists how often injections were given, never how much. Status comes from ClinicalTrials.gov, checked September 15, 2026.

Other Phase 3 trials test MariTide against placebo for heart and blood vessel events (MARITIME-CV, NCT07037433), heart failure (MARITIME-HF, NCT07037459), sleep apnea (MARITIME-OSA-1, NCT07225686, and MARITIME-OSA-2, NCT07226765), and obesity in Japan (MARITIME-3-J, NCT06987695). A Phase 2b trial in people with raised liver fat (NCT07441252) gives injections every 4 weeks for 52 weeks. None of these has reported results.

What "monthly", "every 8 weeks" and "quarterly" mean in these studies

The words sound like calendar terms. In the trial records they are fixed week counts.

• "Monthly" means every 4 weeks. The registries write it as Q4W. That works out to about 13 injections a year, not 12.
• Every 8 weeks (Q8W) is about 6 or 7 injections a year. In Phase 2 it was one of the starting schedules. In the extension trials and MARITIME-SWITCH it is a maintenance schedule.
• "Quarterly" means every 12 weeks (Q12W), about 4 or 5 injections a year. It appears only in maintenance settings: Phase 2 Part 2, the MARITIME-1 extension, and, per Amgen, MARITIME-SWITCH.

Amgen's August 2026 release says the drug's long-acting design "supports starting with monthly dosing" and staying on it with "as few as 4 or 6 doses per year". That is the company's goal for the program. It is not yet a finding from a completed Phase 3 trial.

The switch study is worth reading closely. People in it lost weight on a weekly GLP-1 drug first. The question is whether moving to less frequent MariTide holds that loss. It does not test whether MariTide on its own causes that much weight loss, and it has no placebo group.

What the published results show, and what they don't

The one peer-reviewed efficacy result is Phase 2 Part 1. Across the MariTide groups, people without diabetes lost an average of 12.3% to 16.2% of body weight at 52 weeks, against 2.5% on placebo. People with type 2 diabetes lost 8.4% to 12.3%, against 1.7%. Their HbA1c fell by 1.2 to 1.6 percentage points, against a change of 0.1 points on placebo.

Those figures come from the journal's main analysis, which counts everyone who was randomized, including people who stopped treatment. Amgen's press releases have quoted higher "up to about 20%" figures. Those use a different way of analysing the same data, so the two sets of numbers are not in conflict, but they are not interchangeable either.

Side effects. Gut side effects such as nausea and vomiting were common. The paper says they were less frequent when treatment began at a lower level and was increased step by step. The authors reported no unexpected safety signals. A one-year trial of a few hundred people cannot rule out rarer problems.

The every-8-week starting group. It was part of Phase 2, but the published abstract reports a range across all groups and does not give a separate figure for that group. We have not reported one here.

Year two. Amgen says most Phase 2 participants kept their weight off for another 52 weeks on monthly or every-12-week injections, with very low rates of nausea and vomiting. That is a company statement from February 2026. We found no journal paper or posted registry results with the numbers behind it.

What is still unknown

• Durability. No Phase 3 trial has shown whether injections every 8 or 12 weeks keep weight off. The extension trials are not expected to reach their main endpoint before late 2027, and MARITIME-SWITCH before early 2028, per registry estimates.
• Tolerability after a switch. Moving from a weekly drug to a long-acting one is a new situation. MARITIME-SWITCH tracks side effects for up to 84 weeks, but nothing has reported.
• How many people qualify. The maintenance trials only enroll people who already lost weight and finished earlier treatment. Results, when they come, will describe that group, not everyone starting out.
• Cross-trial comparisons. It is tempting to line MariTide's numbers up against semaglutide or tirzepatide. Different trials enroll different people, run for different lengths, and use different analyses. Only a head-to-head trial can answer which works better, and none has been done.
• Registry details. The MARITIME-SWITCH record calls the trial open-label in its full title, yet lists participants and investigators as masked. The two schedules are not named in the registry. We rely on Amgen's description for the every-8-week and quarterly wording.
• Long-term safety. Large outcome trials in heart disease and heart failure are running, with primary completion estimated for mid-2028.

What this does not mean