Once-Monthly Weight-Loss Injections: What the Science Actually Says

A clear look at MariTide and the push toward once-monthly obesity shots, why the idea is promising, and why weekly GLP-1s are still the only approved injectables.

Maybe you have settled into a weekly injection routine, or you are still deciding whether to start one at all. Either way, you have probably seen the headlines: a weight-loss shot you might take just once a month instead of once a week. It is a genuinely interesting idea, and it is easy to oversell. Here is where the science actually stands, what monthly dosing would and would not change, and why, for now, the only injectable options a physician can prescribe are still the weekly ones.

What "once a month" would actually change

Today's approved GLP-1 injectables are weekly medicines. If you take semaglutide (the active ingredient in Ozempic and Wegovy, which are Novo Nordisk brands) or tirzepatide, you have a set day each week, and that rhythm becomes part of your routine. We walk through that cadence in our guide to the weekly dosing schedule. A once-monthly medicine would mean roughly twelve injections a year instead of about fifty-two.

For some people that sounds like a small difference. For others, it is not small at all. Fewer injections can mean fewer moments of dread for anyone who finds needles genuinely hard, something we cover in our piece on injection anxiety. It can also mean fewer chances to forget a dose during a busy stretch. But convenience here is a hypothesis being tested, not a settled advantage. No study has shown that monthly dosing produces more weight loss than weekly dosing. The honest framing is simple: monthly injections might be easier for some people to stay consistent with, and better consistency could matter over the long run. That is a reasonable idea, not yet an established fact.

The drug leading the pack

The most advanced once-monthly candidate is MariTide, also called maridebart cafraglutide, developed by Amgen. The first thing to be clear about: MariTide is investigational. It is not FDA-approved, it is not available by prescription, and it exists today only inside clinical trials. If you read anything suggesting you can get it right now, that is not accurate.

What makes it unusual is how it is built. MariTide is a bispecific peptide-antibody conjugate. In plain terms, it pairs a GLP-1 receptor agonist, the same broad target as today's medicines, with a component that acts on a second receptor called GIP. Here is a detail worth getting right, because it is easy to garble: MariTide blocks the GIP receptor, while tirzepatide (the active ingredient in Mounjaro and Zepbound, which are Eli Lilly brands) activates it. Two serious programs are taking opposite approaches to the same receptor, which tells you how much is still being worked out here.

What the Phase 2 trial actually showed

MariTide's mid-stage results were published in a peer-reviewed medical journal in 2025. In that dose-ranging trial, the drug was given as a subcutaneous injection once every four weeks, and one group was dosed once every eight weeks, a stark contrast to the weekly schedule of current medicines. Among adults with obesity and no diabetes, 465 participants, the average weight change at 52 weeks ranged from about 12.3 percent to 16.2 percent depending on dose, in the trial's primary analysis, compared with 2.5 percent on placebo. Notably, weight loss had not plateaued at the 52-week mark. In a separate group of 127 people who had both obesity and type 2 diabetes, the average change ranged from about 8.4 percent to 12.3 percent versus 1.7 percent on placebo, with HbA1c (a long-term blood sugar measure) falling by roughly 1.2 to 1.6 percentage points in the primary analysis.

You may also see a bigger headline number, something like "up to about 20 percent." That figure comes from a different way of analyzing the same data, an on-treatment analysis that focuses on people who stayed on the drug as directed. It is real, but it is not the primary result and not what a typical person should expect. The more conservative primary analysis put the top of the obesity range near 16 percent. These are averages from an early study, and individual results vary a great deal.

Why an antibody lets the dose stretch out

How can one injection last a month? The answer is in that antibody structure. Antibodies clear from the body slowly, in part through a natural recycling process, so a drug built around one stays active far longer than a typical peptide. Secondary reporting has put MariTide's half-life at roughly 21 days, about three weeks, on the order of three times longer than the weekly GLP-1 class. That long duration of action is what makes monthly, or in one trial arm every-other-month, dosing even plausible. It is a clever piece of engineering, and it is also part of why the side-effect timing looks a little different.

The side-effect picture you should not gloss over

The most common side effects in the Phase 2 trial were gastrointestinal: nausea, vomiting, and constipation. That will sound familiar to anyone who has taken a GLP-1. Most of these events were mild and eased with time, and they clustered around the first dose. Researchers found that starting at a lower dose and stepping up gradually reduced how often they happened. Even so, some participants stopped the drug, and the rates of vomiting and discontinuation were high enough that the team revised the dose-escalation plan for the larger Phase 3 studies. This is not a footnote. A medicine that is easier to remember does you little good if the early doses are hard to tolerate, and how a monthly drug should be started is exactly what later trials are built to answer.

Where this sits in development

MariTide is now in Phase 3, the stage where a drug is tested in much larger groups over longer periods. The program is called MARITIME. Two of its studies, one in obesity and overweight and one in type 2 diabetes, are 72-week chronic weight-management trials, and additional outcome studies in cardiovascular disease, heart failure, and obstructive sleep apnea were planned as well. Phase 3 is the real test. Plenty of promising mid-stage drugs look different once they are studied in thousands of people. Timelines here are estimates, not promises, and no approval date is set. MariTide is one part of a crowded field; for the wider view, our overview of the 2026 weight-loss pipeline maps out the other candidates.

What is monthly, and what only sounds like it

It is easy to lump every new drug together, so a quick word on the difference. MariTide is by far the most advanced monthly candidate. Behind it, and much earlier in development, is MBX 4291 from MBX Biosciences, a once-monthly GLP-1/GIP co-agonist in Phase 1, with its first 12-week readout expected around the end of 2026. That is very early, and a lot can change. Meanwhile, some drugs described as next-generation are not monthly at all. Amycretin, for instance, is a Novo Nordisk candidate dosed weekly by injection or taken as a daily pill, not monthly. When you read about the future of these medicines, the dosing interval is worth checking for yourself, because the headlines do not always make it clear.

What this means for you right now

If you are on a GLP-1 today, or weighing whether to start, the practical takeaway is steady: the injectable medicines a physician can actually prescribe are the weekly ones, semaglutide and tirzepatide. Monthly dosing is a real and promising direction, but it lives in clinical trials for now, and the questions that matter most, how well it works over years and how comfortably people tolerate it, are still being answered.

None of this changes the fundamentals of good care. Whatever the dosing schedule, these medicines work best as part of a managed plan rather than a quick fix, and most people stay on treatment longer than they first expect, which we walk through in our piece on how long people stay on a GLP-1. And you should never start, stop, or change any medication on your own; that decision belongs with your prescriber, who knows your history. If a once-monthly option earns FDA approval down the road, Dr. Anjmun Sharma, MD, and the team will evaluate it the way we evaluate everything: carefully, honestly, and with your individual situation in mind. This article is for information, not medical advice, and results vary from person to person.

Frequently asked questions

This article is informational only and not medical advice. Speak with a licensed physician before starting or changing any GLP-1 therapy. Individual results vary. New Hope Weight Loss is a physician-supervised medical weight loss clinic in Costa Mesa, CA. Eligibility for treatment is determined during the medical consultation. Compounded semaglutide and compounded tirzepatide are not the same products as Wegovy®, Ozempic®, Mounjaro®, or Zepbound®.