Pemvidutide (Altimmune): GLP-1/Glucagon Dual Agonist Weight-Loss Evidence

Pemvidutide is an investigational once-weekly injectable from Altimmune that activates two receptors at once: the GLP-1 receptor and the glucagon receptor. That second target puts it in the same emerging class as mazdutide and survodutide and sets it apart from semaglutide and tirzepatide — glucagon agonism is meant to raise energy expenditure and pull fat directly out of the liver on top of the appetite suppression that GLP-1 drugs already deliver. Pemvidutide is being developed on two parallel tracks: obesity (the phase 2 MOMENTUM trial) and metabolic dysfunction-associated steatohepatitis (MASH), where its phase 2b IMPACT trial reported results in late 2025. It is not FDA-approved and is not available outside clinical trials. This article covers what pemvidutide is, what MOMENTUM and IMPACT actually showed, the notable body-composition signal, how its weight-loss magnitude compares to the approved drugs, and what its development stage means for patients.

The honest summary

• Pemvidutide is a GLP-1 + glucagon dual agonist. A single peptide activates both the GLP-1 receptor (appetite suppression, slowed gastric emptying, glucose-dependent insulin release) and the glucagon receptor (increased energy expenditure and direct hepatic fat oxidation). It is dosed once weekly by subcutaneous injection, and in MASH trials it was given without dose titration (Noureddin 2025 Lancet^[1], Harrison 2025 J Hepatol^[2]).
• Investigational, not FDA-approved. As of 2026 pemvidutide has no FDA approval and no approval anywhere. It exists only within Altimmune's clinical-trial program; there is no legal prescription or pharmacy supply.
• The obesity evidence is MOMENTUM. The phase 2 MOMENTUM trial enrolled 391 adults with obesity or overweight (no diabetes) randomized to pemvidutide 1.2 mg, 1.8 mg, 2.4 mg, or placebo for 48 weeks. Altimmune's topline disclosure reported mean weight loss of 15.6% on the 2.4 mg dose at week 48, with more than 30% of those subjects reaching at least 20% weight loss^[3]. These numbers are a company press release, not a peer-reviewed publication — treat them accordingly.
• The MASH evidence is peer-reviewed. The phase 2b IMPACT trial (Noureddin 2025 Lancet^[1]) randomized 212 patients with biopsy-confirmed F2–F3 MASH; pemvidutide met its MASH-resolution endpoint (52–58% vs 20% on placebo) but did not meet the fibrosis-improvement endpoint at 24 weeks. An earlier phase 1b MASLD study (Harrison 2025 J Hepatol^[2]) showed significant reductions in liver-fat content and body weight.
• Magnitude lands near semaglutide. MOMENTUM's 2.4 mg result (−15.6% at 48 weeks) is in the range of semaglutide's STEP-1 (−14.9% at 68 weeks, Wilding 2021^[4]) and below tirzepatide's SURMOUNT-1 top dose (−20.9% at 72 weeks, Jastreboff 2022^[5]) — though cross-trial comparison is imperfect given different populations, timepoints, and the fact that pemvidutide's number is from a smaller phase 2.
• Its standout claim is body composition. Altimmune has emphasized that a high proportion of the weight lost on pemvidutide is fat rather than lean mass, attributed to the glucagon component. This is a real area of interest for the whole field, but the supporting data are early and not yet a peer-reviewed head-to-head against other drugs.

What pemvidutide actually is, pharmacologically

Pemvidutide is a long-acting peptide engineered to activate both the GLP-1 receptor and the glucagon receptor in a fixed ratio. The GLP-1 side shares its core action with semaglutide and liraglutide: glucose-dependent insulin secretion, delayed gastric emptying, and hypothalamic satiety signaling that suppresses appetite. The glucagon side — the part that distinguishes pemvidutide from a pure GLP-1 drug — acts directly on the liver to stimulate fatty-acid oxidation and inhibit lipogenesis, and is thought to add a modest increase in energy expenditure on top of the appetite effect.

The pairing is deliberately counterintuitive. Glucagon is best known as the hormone that raises blood sugar, so adding glucagon agonism to a weight-loss drug seems backwards. The rationale, spelled out in pemvidutide's own MASLD paper (Harrison 2025^[2]), is that the GLP-1 component's insulin-secreting and appetite-suppressing effects offset glucagon's glycemic downside, while glucagon's direct hepatic action provides a more potent mechanism for liver-fat reduction than weight loss alone. This is the same engineering logic behind mazdutide and survodutide, and behind the glucagon arm of retatrutide's triple agonism. Altimmune also designed pemvidutide to be given without the slow dose-escalation ramp most incretin drugs require — in the IMPACT trial it was administered at full dose from the start.

The obesity evidence: the MOMENTUM phase 2 trial

MOMENTUM is pemvidutide's pivotal obesity study to date. It enrolled 391 adults with obesity, or overweight with at least one weight-related comorbidity, who did not have diabetes. Participants were randomized 1:1:1:1 to once-weekly subcutaneous pemvidutide 1.2 mg, 1.8 mg, 2.4 mg, or placebo for 48 weeks, alongside diet and exercise. According to Altimmune's topline disclosure^[3], the 2.4 mg dose produced a mean body-weight reduction of 15.6% at week 48 — roughly 32 pounds on average — with the weight curve still declining at the end of treatment, and more than 30% of subjects on that dose reaching at least 20% weight loss.

The body-composition angle: fat loss vs lean loss

The most distinctive marketing and scientific claim around pemvidutide is body composition. A recurring concern with all potent weight-loss drugs is that a meaningful share of the weight lost is lean mass (muscle) rather than fat — an issue prominent enough that obesity-therapy trialists are now debating muscle preservation as a formal regulatory endpoint (von Haehling 2025^[6]). Altimmune has positioned pemvidutide's glucagon-driven mechanism as preferentially mobilizing fat, reporting that a high proportion of the weight lost is fat mass with relative preservation of lean mass. The biological rationale is sound — glucagon acts directly on hepatic and adipose fat metabolism — but the comparative data establishing a body-composition advantage over semaglutide or tirzepatide are early and not yet settled in peer-reviewed head-to-head trials. It is a promising signal, not a proven differentiator.

The MASH track: the IMPACT phase 2b trial

Pemvidutide's second development track is metabolic dysfunction-associated steatohepatitis (MASH), the progressive form of fatty liver disease, where the glucagon component's direct hepatic action is the central rationale. IMPACT (Noureddin 2025 Lancet^[1]) is a phase 2b trial that randomized 212 patients with biopsy-confirmed F2 or F3 MASH across 83 sites in the US and Australia to once-weekly pemvidutide 1.2 mg, 1.8 mg, or placebo, given without dose titration. The dual primary endpoints were MASH resolution without worsening of fibrosis, and at least one-stage fibrosis improvement without worsening of MASH, both assessed at 24 weeks.

Pemvidutide met the first endpoint convincingly: MASH resolution without fibrosis worsening occurred in 58% of the 1.2 mg group and 52% of the 1.8 mg group, versus 20% on placebo (both p<0.0001). It did not meet the second endpoint — fibrosis improvement reached 33% (1.2 mg) and 36% (1.8 mg) versus 28% on placebo, differences that were not statistically significant at 24 weeks. The drug was well tolerated, with adverse events mostly mild or moderate and very low discontinuation rates. The investigators noted that longer-duration trials are planned, since fibrosis regression typically lags inflammatory resolution. An earlier phase 1b MASLD study (Harrison 2025 J Hepatol^[2]) in 94 patients had already shown significant reductions in liver-fat content, hepatic inflammation markers, and body weight.

Magnitude: pemvidutide vs the approved drugs

The fair reading is that pemvidutide's 2.4 mg arm at 48 weeks (−15.6%) sits right around semaglutide's STEP-1 result and below tirzepatide's top dose. But two caveats matter beyond the usual cross-trial warnings. First, MOMENTUM is a phase 2 trial of 391 people reported via press release, while STEP-1 and SURMOUNT-1 are large peer-reviewed phase 3 trials — the evidentiary tiers are not equal. Second, the comparison that pemvidutide's developers care most about is not the headline percentage but the quality of the weight lost (fat vs lean) and the liver-fat effect, neither of which a single scale-weight number captures. Read the magnitude chart as directional placement, not a verdict.

What the development stage means for patients

Pemvidutide is genuinely interesting science: a GLP-1/glucagon dual agonist with semaglutide-range weight loss, a strong MASH-resolution signal, and a plausible body-composition story. But interesting science is not an available medicine. As of 2026 pemvidutide has no FDA approval, no approval anywhere, and exists only inside Altimmune's clinical-trial program. A path to market would require a successful phase 3 obesity program and full FDA review, neither of which had produced an approval at the time of writing.

The practical takeaway for someone researching pemvidutide is that the relevant, prescribable options remain the approved drugs: semaglutide (Wegovy/Ozempic, STEP-1^[4]) and tirzepatide (Zepbound/Mounjaro, SURMOUNT-1^[5]). Anything marketed as “pemvidutide” through research-peptide channels is operating entirely outside any approved or trial supply chain and carries the identity, purity, and dosing risks that come with unregulated peptides. The honest answer to “can I get pemvidutide?” in 2026 is: only by enrolling in a clinical trial. Talk to a clinician about the approved drugs, and watch the MOMENTUM full publication and any phase 3 readouts for where pemvidutide actually lands.