Efimosfermin alfa dosage and evidence
Written by Aaron CuhaReviewed Sep 2026
The short answer
Efimosfermin alfa is GSK's monthly copy of FGF21, a liver hormone. GSK bought it for $1.2 billion up front. The FDA gave it a Breakthrough Therapy label for fatty liver disease, and mid-stage results were published in 2026.
Evidence grade for Efimosfermin alfa: Moderate. The rule: at least one finished study in people, and at least 100 people who took it. The sum on this page: 2 completed trials, 186 people given it. A grade counts how much has been done to people, not whether it works.
- People given it
- 186
- Human studies
- 2
- Found nothing
- 0
Dose
No human dose established
Amounts that were given in studies sit in Human evidence on this page. None of them is a personal dose.
2 completed trials, 186 people given it
2 effects reported, 1 unwanted, 1 wanted, by people using it, not a trial
Goal pages: Fat loss and metabolism, Ageing and longevity, Gut health
In plain English
In plain English, from Aaron
This is how I would explain it to a friend. The evidence, with the numbers, is further down the page.
Efimosfermin is a monthly shot that copies FGF21, a liver hormone. GSK bought it for $1.2 billion up front. It is being tested for fatty liver disease. The FDA gave it a label that speeds up review. It is not approved.
What people take it for
- Treating fatty liver disease with one shot a month.
- Cutting liver fat.
What studies in people showed
In a 12-week study of 102 people with fatty liver disease, 89 percent on the drug cut their liver fat by at least 30 percent. On a dummy shot, 7 percent did. In a 24-week study of 84 people with liver scarring, the monthly shot was well tolerated. The published summary of that study reports safety only, not whether scarring got better. Side effects were mostly mild stomach upset, nausea and diarrhoea.
What people report
Reports, not study results
The good
- In the study on this page, liver fat fell sharply in most people on the drug.
The bad
- Mild stomach upset, nausea and diarrhoea were the main side effects in the studies on this page.
Where these come from: Both lines are from the studies on this page. We have not collected forum or user reports for this drug yet.
My bottom line
Liver fat on a scan is not scarring on a biopsy. Check your liver numbers, and treat this as a maybe.
An opinion, not a finding. I am a coach, not a doctor.
What it has been measured to do
Measured in people
Goals Efimosfermin alfa has been tested for in people, biggest studies first. We count only what the studies on this page say, so the real numbers may be higher.
- Liver fat and liver health102 people · 1 study
- Living longer102 people · 1 study
34 of the 36 indexed goals have no study of any kind behind Efimosfermin alfa
No study in people, animals or cells on this page reports a result for these. That does not prove Efimosfermin alfa does nothing for them. It does mean anything you have heard about Efimosfermin alfa and one of these did not come from a study cited here.
Show full evidence
What is Efimosfermin alfa?
Efimosfermin alfa is GSK's monthly copy of FGF21, a liver hormone. GSK bought it for $1.2 billion up front. The FDA gave it a Breakthrough Therapy label for fatty liver disease, and mid-stage results were published in 2026.
Efimosfermin is a lab-made copy of FGF21 that lasts long enough for one shot a month. It is the only monthly drug of this kind in development. GSK bought it for $1.2 billion up front. In a 12-week study of 102 people with fatty liver disease, 89 percent on the drug cut their liver fat by at least 30 percent, against 7 percent on a dummy shot. Its 24-week mid-stage study in fatty liver disease with moderate or advanced scarring was well tolerated. Its published summary reports safety only, not what the liver samples showed. Other early data back the monthly schedule. The FDA gave it Breakthrough Therapy status and Europe's regulator gave it PRIME status, both of which speed up review. GSK is preparing large final-stage studies. Like other FGF21 drugs, it is aimed at liver disease and metabolic health, not weight. Its effect on weight is modest.
How does Efimosfermin alfa work?
It turns on the FGF21 receptor for a long time. That lowers liver fat, inflammation and scarring.
The evidence, in charts
Fig. 1a · how many people
186people, across 2 studies in people cited here
| Study | People | Share |
|---|---|---|
| The Lancet Gastroenterology and Hepatology 2025 | 102 | 55% |
| PubMed 2026 | 84 | 45% |
One study holds 55% of these people, so the total rests more on one study than its size suggests. Counts are the number of people each study on this page says it signed up. That includes studies that only watched people and gave nobody the compound. 1 more study in people gives no headcount and is not counted here. Studies still signing people up are left out, and only studies cited on this page are counted.
Fig. 1b · evidence mix
All 3 sources here are studies in people.
- Study in people · done in people3100%
Counted from the list of sources on this page. It counts only what we cite, so there may be more studies out there. A review counts once, however many studies it sums up.
Fig. 2 · evidence over time
Sources here come from just two years, 2025 and 2026.
Too few different years on this page to draw a timeline.
Fig. 3 · legal status at a glance
US
Not approved
UK
Not approved
AU
Not approved
CA
Not approved
Not approved in any of the four countries shown. This is what the law says, not a verdict on the science. See Legal status below for the full text and any notes.
Fig. 4 · how much does what
Nobody has tested different amounts in people
This chart would show how the effect changes as the amount goes up. For this compound, nobody has measured that in people. So we leave it empty. We will not borrow an animal chart and pretend it works the same in people.
Fig. 5 · what the molecule is
- Kind of compound
- Biologic
- Molecule weight
- 89,093 Da (Fc-FGF21 fusion protein)
- Half-life
- Stated in words, not a numbersee the exact wording below
- Chain length
- None on file
No amino acid sequence is on file for Efimosfermin alfa, so none is drawn rather than guessed from a name.
The studies we cite
- Study in people2026Efimosfermin alfa in MASH with F2/F3 fibrosis: Phase 2
A monthly shot was well tolerated in a small study. The published summary reports safety, not a scarring result. 84 people with fatty liver disease and moderate or advanced scarring got efimosfermin once a month or a dummy shot for 24 weeks. Side effects were mostly mild stomach upset in the first few weeks, and nobody was seriously harmed. The study was built to look for harm, not to prove the drug clears scarring. The makers paid for it.
84 adults with biopsy confirmed MASH and F2 or F3 fibrosis randomised to efimosfermin 300 mg every four weeks (n = 43) or placebo (n = 41), 24 weeks. The published abstract reports safety and tolerability only: adverse events in 67 percent on drug against 55 percent on placebo, mostly mild or moderate, most commonly transient gastrointestinal events. 65 participants had evaluable week 24 biopsies but the abstract reports no histology outcome. The authors conclude only that monthly dosing was generally well tolerated. This page previously claimed histologic improvement, which the abstract does not support.
- Study in people2025Efimosfermin alfa (BOS-580), a long-acting FGF21 analogue, in participants with phenotypic metabolic dysfunction-associated steatohepatitis: a multicentre, randomised, double-blind, placebo-controlled, phase 2a trial
Liver fat fell sharply. 102 people with fatty liver disease got efimosfermin or a dummy shot for 12 weeks. By week 12, 89 percent of those on the drug had cut their liver fat by at least 30 percent, against 7 percent on the dummy. Side effects were mostly mild nausea and diarrhoea. Liver fat on a scan is not scarring on a biopsy, and 12 weeks is short. Boston Pharmaceuticals paid for the study.
102 participants, 12 weeks, phase 2a with safety and tolerability as the stated primary measure and efficacy only as exploratory biomarkers. At week 12, 47 of 53 evaluable participants on efimosfermin (89 percent) had at least a 30 percent reduction in liver fat fraction against 2 of 30 (7 percent) on placebo. Gastrointestinal events were the commonest adverse event, 40 percent against 24 percent, with no treatment related deaths. Funded by Boston Pharmaceuticals.
- Study in people2025GSK's efimosfermin receives FDA Breakthrough Therapy designation
This is a regulatory label, not evidence. The FDA gave efimosfermin Breakthrough Therapy designation, which speeds up meetings and review for drugs that look promising early. It is granted on preliminary data. It is not an approval, not a finding, and not a judgement that the drug works. Europe granted a similar status. The drug still has to pass its large trials.
Regulatory acceleration for MASH.
Common questions
Has Efimosfermin alfa been tested in people?
Yes. 186 people given it across 2 completed trials cited here, 0 of which found nothing. Efimosfermin alfa is GSK's monthly copy of FGF21, a liver hormone. GSK bought it for $1.2 billion up front. The FDA gave it a Breakthrough Therapy label for fatty liver disease, and mid-stage results were published in 2026.
What is the Efimosfermin alfa dosage?
No human dose established. Amounts that were given in studies sit in Human evidence on this page. None of them is a personal dose. 2 completed trials, 186 people given it
Is Efimosfermin alfa FDA-approved?
Investigational; the FDA gave it Breakthrough Therapy status, which can speed up its review
Is efimosfermin a weight-loss drug?
No. Like other FGF21 drugs, it is aimed at liver disease and metabolic health. Its effect on weight is modest.