Is Imeglimin Better Than Metformin for Lifters?

Imeglimin is starting to show up in the same conversations as MOTS-c and NAD+, and the pitch writes itself. It's a cousin of metformin, it works on your mitochondria, it raises NAD+, and it supposedly does all of that without the stomach problems, the lactic acidosis risk, or the blunted gains that make lifters nervous about metformin. Think of it as a pharmaceutical blend of metformin, MOTS-c and NAD+ in one tablet.

Some of that is true. Some of it is a mouse study wearing a lab coat. This article sorts the two, using the actual trial data, and finishes with the bloodwork you'd need to tell whether it's doing anything for you.

What imeglimin actually is

Imeglimin is the first drug in a class called the "glimins", a small molecule from the tetrahydrotriazine family. It shares a chemical fragment with metformin, which is where the "cousin" label comes from, but it isn't a biguanide and it doesn't behave like one (Chevalier et al., 2023). Japan approved it for type 2 diabetes in 2021 under the brand Twymeeg (Lamb, 2021). India followed in late 2022, and Indian generics such as Imeglyn are now where most grey-market tablets come from.

The label dose in Japan is 1,000 mg twice a day. That is a diabetes dose for diabetic patients, not a recommendation for anyone else.

Pharmacologically it's a fairly clean drug. Its half-life is 9 to 20 hours in Western subjects and 4.5 to 12 hours in Japanese subjects, food doesn't change absorption, and it isn't processed by the liver's CYP enzymes, so it doesn't interact with much (Fouqueray et al., 2022). It leaves the body almost entirely unchanged in urine. That last point matters more for lifters than anything in the marketing, and we'll come back to it.

Is it really metformin plus MOTS-c plus NAD+?

Each row is something imeglimin is claimed to do, with the best evidence behind it.

So the framing is half right.

The NAD+ part comes from rodent islet work. In beta cells isolated from diabetic rodents, imeglimin enlarged the NAD+ pool, "potentially" through the NAMPT salvage pathway, and that amplified insulin release in response to glucose (Hallakou-Bozec et al., 2021). That is NAD+ inside pancreatic cells, not a whole-body NAD+ boost, and the paper's authors are employees of the company that developed the drug. For context, oral nicotinamide riboside at 2,000 mg a day for 12 weeks did not raise muscle NAD+ or improve clamp-measured insulin sensitivity in obese, insulin-resistant men (Dollerup et al., 2018; Dollerup et al., 2020). Raising NAD+ in one tissue in a dish and changing your physique are very different claims.

The metformin part is where the two drugs overlap: they hit the same machinery in different ways. Metformin is a well-established inhibitor of mitochondrial Complex I. Imeglimin also partially inhibits Complex I, but the effect is much milder. In intact rat liver cells, metformin cut oxygen consumption and imeglimin didn't (Vial et al., 2021). In an independent lab, imeglimin did activate AMPK in liver cells, just less strongly than metformin (Hozumi et al., 2023). So imeglimin is a gentler mitochondrial brake, not a different engine.

The MOTS-c part is mostly vibes. MOTS-c's best-characterised action is AMPK and PGC-1α signalling in mouse muscle, and nobody has shown imeglimin activating AMPK in muscle. If you want the MOTS-c evidence on its own terms, our MOTS-c and SS-31 breakdown covers it.

The one thing imeglimin does that metformin doesn't

Metformin mostly works by lowering how much glucose your liver pumps out. Imeglimin's main human effect is on the pancreas. In a 7-day clamp study, it raised the glucose-stimulated insulin response by 112% and improved beta-cell glucose sensitivity by 36% (Pacini et al., 2015). That effect depends on glucose being high, which is why hypoglycaemia rates in trials were close to placebo, even on top of insulin.

The best human insulin-sensitivity data is newer. In 22 Japanese men with type 2 diabetes taking 2,000 mg a day for 20 weeks, the glucose area under an oral glucose tolerance test fell by a median 108.6 mg·h/dL, and in the 16 who had clamps, insulin sensitivity improved in skeletal muscle, liver and fat (Tajima et al., 2026). That's genuinely encouraging. It's also 22 men, no placebo group, all diabetic, and sponsor-funded.

Is imeglimin better than metformin?

Start with what it does against placebo, because those are the strongest trials.

Sources: Dubourg et al., 2021; Reilhac et al., 2022; Fouqueray et al., 2013; Dubourg et al., 2022.

Those are solid numbers for a diabetes drug, roughly in metformin's range. But "better than metformin" needs head-to-head trials, and there are only two small ones.

In an Osaka trial, imeglimin at 2,000 mg a day and metformin at 1,000 mg a day lowered HbA1c by a "similar" amount over 24 weeks. Imeglimin raised insulin and the incretin GIP, while both raised GLP-1 (Usui et al., 2025). The metformin dose was low, which flatters imeglimin.

In the MEGMI trial, people already on a DPP-4 inhibitor plus low-dose metformin either added imeglimin or increased their metformin. Imeglimin won, 7.61% to 6.93% versus 7.56% to 7.09%, a difference of 0.21%. It also lowered body weight and liver enzymes. But 7 of the 33 people on imeglimin stopped because of serious gut side effects (Takahashi et al., 2025).

So: about as good as metformin, a little better in one setting, with no long-term outcome data at all. Metformin has decades of safety history and costs almost nothing.

Does imeglimin avoid metformin's stomach problems?

On its own, mostly yes. Gut side effects were low in the monotherapy trials. The problem is stacking them. In a retrospective Japanese study, 38% of people taking imeglimin with metformin had gut side effects, against 11% of those taking imeglimin without it (Ito et al., 2025). A post-hoc analysis of TIMES 2 found 40.6% of the metformin combination group had gut symptoms, mostly mild and mostly in the first four months (Ito et al., 2025).

If metformin wrecks your stomach, imeglimin alone might be a reasonable swap. Running both is where the trouble starts.

Is the lactic acidosis risk really lower?

In animals, clearly. In a dog surgical model and a rat model of kidney injury, only metformin raised lactate, dropped blood pH and caused deaths at the top dose. Metformin also inhibited Complex I far more than imeglimin at similar plasma levels (Theurey et al., 2022). Every author on that paper worked for, or was funded by, the developer.

In humans, there is no controlled lactate comparison. That doesn't mean it's dangerous. It means "safer than metformin" is a reasonable hypothesis, not a finding.

Will imeglimin blunt your gains like metformin can?

This is the real reason lifters go looking for a metformin alternative, so here's what the metformin data actually says.

In the MASTERS trial, healthy adults aged 65 and older did 14 weeks of supervised resistance training on 1,700 mg a day of metformin or placebo. Lean mass rose 1.95% on placebo against 0.41% on metformin, and thigh muscle 3.90% against 0.45% (Walton et al., 2019). Fat loss was the same in both groups, and the strength difference was only a trend. In a separate trial, 53 adults around 62 years old did 12 weeks of aerobic training. Metformin blunted the gains in insulin sensitivity and VO2 max, and wiped out the training-driven increase in muscle mitochondrial respiration (Konopka et al., 2019). The leading explanation is metformin's Complex I inhibition, the exact signal exercise uses to build more mitochondria.

Both trials were in older adults, not 30-year-olds on testosterone, but the signal is consistent enough to take seriously.

Now imeglimin. There is no human training study. What exists is animal work:

• In obese mice and 18-month-old mice, imeglimin protected fast-twitch muscle fibre size (+66% and +14% vs untreated controls) and dampened inflammation and oxidative stress genes (Ye et al., 2026). That is protection against atrophy in sick or old animals, not extra growth in healthy ones.
• In mice with fatty-liver-driven muscle wasting, imeglimin preserved muscle mass, grip strength and fibre size, and restored muscle NAMPT and NAD+ (Osaki et al., 2027). This is the clearest data linking imeglimin on its own to muscle NAD+, and it's a disease model.
• In an animal study pairing imeglimin with resistance training, the combination raised muscle NAD+, SIRT1 and SIRT3, PGC-1α and GLUT4 (Ishiguro et al., 2025). The abstract doesn't report what imeglimin did on its own.

Training already does what the NAD+ marketing promises. Three weeks of exercise raised muscle NAMPT by 127% in sedentary adults, and athletes carry about twice as much as untrained people (Costford et al., 2010). The logic for imeglimin is that a weaker Complex I brake should interfere less with that exercise signal than metformin's stronger one. But imeglimin still touches Complex I, and "should" is doing all the work in that sentence.

Does imeglimin improve nutrient partitioning?

For this to count, imeglimin would need to push more glucose into muscle instead of fat, and show it as better body composition at the same calorie intake. Here's what exists:

• Muscle insulin sensitivity improved in the 22-man clamp study above. That's the right direction, in diabetic muscle.
• In a 28-patient pilot of people with fatty liver and type 2 diabetes, six months of imeglimin lowered body weight and body fat percentage, with no significant change in skeletal muscle mass on bioimpedance (Fujita et al., 2026). No control group, and "no significant change" in 28 people isn't proof that muscle was spared.
• Elsewhere, weight changes are small, about a kilogram, and mostly seen in people also taking metformin (Ito et al., 2025).
• There are zero body composition studies in lean or trained people.

So the honest answer is that nobody knows. If someone tells you imeglimin is a partitioning agent, ask for the DEXA data. There isn't any.

What if my HOMA-IR reads 3.1 on MK-677 or GH?

This is the scenario most lifters actually land in. You're running MK-677 or GH, your fasting numbers creep up, and you start shopping for a fix.

HOMA-IR is (fasting glucose in mmol/L × fasting insulin in mIU/L) ÷ 22.5 (Matthews et al., 1985). Say your fasting glucose is 5.4 and your fasting insulin is 13:

5.4 × 13 = 70.2, and 70.2 ÷ 22.5 = 3.12

In a lean lifter whose baseline was 1.0, that's a big move. Here's how I'd think about it, in order:

1. Confirm the number. Retest fasted 8 to 12 hours, no hard training for 24 hours, and no GH injection in the previous 5 hours. One bad draw isn't a trend.
2. Stop and see a doctor if fasting glucose is 7.0 mmol/L or more, or HbA1c is 6.5% or more. That's diabetic territory. Drop the secretagogue, and never reach for insulin to fix it.
3. Reduce the cause first. Cut MK-677 from 25 mg to 10 mg, or lower the GH dose. Our MK-677 blood sugar guide treats a HOMA-IR above 3.0 as a reason to stop MK-677 altogether. Retest in 4 to 6 weeks.
4. Berberine is the over-the-counter option, at 500 mg two to three times daily with meals. In a meta-analysis of 37 trials it lowered fasting glucose by 0.82 mmol/L and HbA1c by 0.63%, with bigger effects at higher starting glucose (Xie et al., 2022). Expect less if you're near normal.
5. Metformin XR, 500 mg with dinner, is the best-evidenced drug step. Check kidney function first and B12 yearly.
6. Imeglimin fits here as an alternative to metformin, not an upgrade. It makes sense only if metformin genuinely doesn't agree with you and a prescriber is involved. Don't stack it on metformin unless you enjoy the bathroom.
7. GLP-1 agonists such as semaglutide, tirzepatide or retatrutide are the heaviest hitters for insulin resistance, at the cost of your appetite during a bulk.

After each step, a HOMA-IR below 2.0 means hold, 2.0 to 2.5 means repeat the test, and above 2.5 means go to the next step or reduce the cause.

The bloodwork to run on imeglimin

This is where imeglimin has two traps that metformin doesn't.

Trap 1: HbA1c may lie to you early on

In the INFINITY trial, 29 patients took imeglimin 2,000 mg a day for six months. Glycoalbumin and 1,5-anhydroglucitol, which track short-term glucose, improved quickly, while HbA1c fell slowly, and the gap lasted about two months. The researchers measured red blood cell lifespan and found it lengthened on imeglimin (Osonoi et al., 2025). It was a small exploratory study, but the logic holds: HbA1c is sugar stuck to haemoglobin, longer-lived cells collect more sugar, so HbA1c can read higher than your real glucose control.

If you're on testosterone, your red cell numbers are already shifting from a higher haematocrit, and if you donate blood for it, your red cells are getting younger. Add imeglimin and HbA1c becomes a muddy number. Use fructosamine for the early check. It reflects the past 2 to 3 weeks of glucose instead of the 6 to 8 weeks or more that HbA1c covers, so it responds to a change much faster (Armbruster, 1987).

Trap 2: your kidneys clear it, and creatinine misleads in lifters

Imeglimin leaves the body unchanged in urine, and its dose has to be cut when eGFR falls between 15 and 45 (Kitamura et al., 2023), to 500 mg twice daily in Japanese dosing models (Tomita et al., 2022). Your eGFR is usually calculated from creatinine, which depends on muscle mass and creatine supplementation. In a small study of bodybuilders (12 steroid users, 12 non-users), creatinine-based eGFR was similar between groups, while cystatin C-based eGFR came out slightly lower in the steroid users, alongside more protein in their urine (Ozkurt et al., 2023). Get cystatin C at baseline. Our cystatin C guide explains why.

Testing schedule

ALT and AST are there because orals and heavy training already move them. A clean baseline lets you tell the cause apart. In MEGMI and in fatty liver mouse models, imeglimin actually lowered liver enzymes, so a rise is worth taking seriously.

Buying imeglimin outside Japan

Twymeeg is a Japanese prescription product. Indian manufacturers, including Zydus (Imeglyn), make generics that are sold by prescription in India, and those are what turn up on import sites. Nothing is registered with the TGA, FDA or EMA, so in most Western countries this is personal import of an unapproved medicine. There's no identity testing on what arrives, no guarantee the tablet contains 500 mg, and no recourse if it doesn't. If you go down this road, the bloodwork above is the only way you'll know whether the tablet is doing anything.

Practical recommendations

• If metformin works for you and your stomach tolerates it, there is no evidence imeglimin is better. Stay put.
• If metformin's gut side effects are the problem, imeglimin alone is a reasonable thing to raise with a prescriber. Don't stack the two.
• If your concern is muscle, the evidence that metformin blunts gains comes from older adults on 1,700 mg a day. Imeglimin's muscle-sparing story is from mice.
• Fix the cause first. If MK-677 or GH is driving your HOMA-IR, lowering the dose beats adding a second drug.
• Track fructosamine early, HbA1c late, and cystatin C before you start.

Key takeaways

• Imeglimin lowers HbA1c by roughly 0.4% to 0.9% in diabetic trials, depending on the design, roughly metformin's range. Head-to-head, it matched low-dose metformin and beat a metformin dose increase by 0.21%.
• Its main human effect is more insulin release when glucose is high, plus improved insulin sensitivity in one small uncontrolled study.
• "Metformin plus MOTS-c plus NAD+" is overselling it. The NAD+ effect is in rodent pancreatic cells, and the MOTS-c comparison has no direct evidence.
• Lower lactic acidosis risk and muscle protection are animal findings. There is no human training study.
• Stacking imeglimin with metformin pushed gut side effects to 38% to 41% in Japanese studies, against 11% without metformin in one of them.
• HbA1c may read high for the first couple of months on imeglimin. Use fructosamine for early checks, and cystatin C for kidney function.

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