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Lexicon
Lexicon

Metformin (Glucophage)

The blood sugar agent with a longevity reputation - and a genuine conflict with a building phase.

3 min read 10 sources

To the sources
Molecule model of glossy dark blue and light blue glass spheres floats above a white podium with a glowing rim, blurred lab flasks with blue liquid behind it, symbolic image for metformin
Compound approved · in the US since 1995

Summary

At a glance

Sources checked on 26 Oct 2026

Diabetes-related endpoints (UKPDS 34)
−32 %

753 overweight people with new type 2 diabetes, against diet alone, median 10.7 years1

All-cause mortality (UKPDS 34)
−36 %

same trial, confidence interval 9 to 55 percent1

New diabetes cases in prediabetes (DPP)
−31 %

3,234 people, against placebo, mean 2.8 years; the lifestyle group reached 58 percent3

Plasma half-life
~6.2 hours

about 90 percent leave the body unchanged via the kidney within 24 hours7

  • Metformin is a biguanide. It throttles glucose production in the liver and improves insulin sensitivity, insulin secretion stays unchanged according to the label.710
  • In UKPDS 34 diabetes-related endpoints fell by 32 percent and all-cause mortality by 36 percent in overweight people with type 2 diabetes.1
  • Ten years after the trial ended the advantage was still measurable (UKPDS 80), although the groups' blood sugar values had converged after one year.2
  • In prediabetes metformin cut new diabetes cases by 31 percent. The lifestyle group of the same trial reached 58 percent.3
  • During strength training older people on metformin gained less lean mass (MASTERS). Over years vitamin B12 is low more often.56
  • According to Drugs@FDA and ChEMBL metformin has been approved since 1995. Everything here is the state of research, not a recommendation.810
Profile

Updated July 2026

How long does it stay in the body?

Share left after one dose, calculated with a half-life of ~6.5 hours

Half-life ~6.5 hours
After 13 hours: 25 %
Hour 7 · 47 %Hour 13 · 25 %Hour 20 · 11.9 %Hour 33 · 3 %

Simplified model without an absorption phase, half-life from the TPD lexicon. The lexicon gives 4 to 9 hours, we calculate with the middle.

Class
Biguanide
Use
Oral

once or twice daily, always with food

Half-life
4 to 9 hours
Training conflict
Partly inhibits mTOR

blunts building adaptation

Monitor
Vitamin B12 with use over months
Contents 12 sections
  1. At a glance
  2. What is metformin?
  3. How it works
  4. Use and dosing
  5. What the research shows
  6. Research status
  7. Side effects
  8. Storage
  9. Related compounds
  10. FAQ
  11. Glossary
  12. Sources

What is metformin?

Metformin lowers blood sugar through two routes: it throttles glucose production in the liver and improves insulin sensitivity in muscle and fat tissue. Unlike insulin or sulfonylureas it does not force blood sugar down, it pulls back an overshooting own production. That is why on its own it practically never causes hypoglycaemia.

Mechanistically a large part runs through inhibition of mitochondrial complex I and the resulting activation of AMPK, the cellular energy sensor. That same pathway is the reason for the longevity reputation and, as set out below, for the conflict with muscle growth.

This information is for research and educational purposes only. No medical advice.

Comparison

Four paths to lower blood sugar

Metformin, SGLT2 inhibitors, GLP-1 agonists and basal insulin act at different points, as stated in the TPD lexicon. Tap a card to open its entry.

Biguanide Metformin (Glucophage) Complex I
SGLT2 inhibitor Jardiance (Empagliflozin) SGLT2 GLP-1 agonist Semaglutide GLP-1R Basal insulin Lantus (Insulin Glargine) INSR

Simplified: metformin slows the liver, SGLT2 inhibitors let sugar out through the kidney, GLP-1 agonists act through the incretin system, insulin replaces the hormone itself. 107

How it works

AMPK is the counterpart of mTOR. AMPK becomes active when the cell reports an energy shortfall and then switches to saving and cleaning up. mTOR becomes active when energy and amino acids are plentiful and switches to building. Metformin pushes that balance towards AMPK.

For metabolism that is good. For a building phase it is exactly the wrong switch, because muscle growth runs through mTOR. Several investigations show smaller strength and muscle gains under metformin at equal training. That is not a marginal finding, it is a direct consequence of the mechanism.

In a diet phase it matters considerably less, since improved insulin sensitivity is the dominant effect there.

Where it acts

Where metformin acted in studies

Tap a point or a card. Colour = target in the mitochondria, grey = observed in studies.

  1. Liver

    Throttles glucose production in the liver7

    Complex I
  2. Gut

    Less glucose uptake, diarrhoea in 53 versus 12 percent7

    Observed in trials
  3. Muscle

    Less lean mass gain during strength training (MASTERS)5

    Observed in trials
  4. Heart

    33 percent fewer heart attacks after 10 years of follow-up (UKPDS 80)2

    Observed in trials
  5. Blood

    B12 low or borderline in 19.1 versus 9.5 percent after 5 years6

    Observed in trials
  6. Kidney

    Excreted unchanged in the urine, longer half-life with weak kidneys7

    Observed in trials

Targets in the ChEMBL database10

Compound CHEMBL1703: two recorded mechanisms, type of action on each card.

Mitochondrial complex I (NADH dehydrogenase), subunit ND1 as representative
Gene
MT-ND1
UniProt
P03886
ChEMBL
CHEMBL2363065
Action
Inhibitor, direct binding (ChEMBL lists 50 subunits)
Mitochondrial glycerol-3-phosphate dehydrogenase
Gene
GPD2
UniProt
P43304
ChEMBL
CHEMBL3391681
Action
Inhibitor, direct binding
Translucent light blue cell with a nucleus and several mitochondria, in the centre a glowing blue mitochondrion with a bright spot of light at a turquoise structure, next to it two small blue molecule models
Metformin slows complex I in the mitochondria, the cell reports an energy shortfall. Symbolic image.

Use and dosing

Dosing

Dosing, titration and syringe

Loading the dosing information …

  • Getting started and stepping up, drawn as a staircase
  • Units on the U-100 syringe for every step
  • How long one vial lasts
White folding box with the TPD logo next to a blister of ten round white tablets, two loose tablets in front on a bright lab bench
Tablets in a blister. Symbolic image.

What the research shows

UKPDS 34 (Lancet 1998) is the trial that made metformin a first-line agent. In overweight type 2 diabetics it cut diabetes-related endpoints by 32 percent and all-cause mortality by 36 percent. It did so better than other agents at equal blood sugar reduction.

UKPDS 80 (NEJM 2008) followed participants for ten years after the trial ended. The advantage persisted, even though the groups' blood sugar values had long since converged. This legacy effect is one of the most interesting findings in diabetology.

DPP (NEJM 2002) tested prevention in prediabetes: metformin cut new diabetes cases by 31 percent. The lifestyle intervention in the same trial achieved 58 percent, nearly double. That belongs in an honest account, because the more effective measure was not the drug.

The 2014 observational study (Diabetes Obes Metab) is the origin of the longevity hype: in that analysis, diabetics on metformin outlived matched non-diabetics. That is a striking finding, but it is an observational study and not proof of efficacy. The randomised longevity trial is still outstanding.

Study results

What the trials measured

Interactive: switch tabs, tap points, show or hide arms. Arms are named relative to each other, no dosing advice.

Fewer events in type 2 diabetes12

Relative risk reduction against diet alone, values from the abstracts

Any diabetes-related endpoint1 UKPDS 34, median 10.7 years
Metformin -32%
Diabetes-related death1 UKPDS 34
Metformin -42%
All-cause mortality1 UKPDS 34
Metformin -36%
Any diabetes-related endpoint2 UKPDS 80, 10-year follow-up
Metformin, 10 years after trial end -21%
Myocardial infarction2 UKPDS 80
Metformin, 10 years after trial end -33%
All-cause mortality2 UKPDS 80
Metformin, 10 years after trial end -27%

Median HbA1c was 7.4 instead of 8.0 percent on metformin. In the follow-up the HbA1c differences were gone after the first year, the risk reduction remained.

Fewer new diabetes cases in prediabetes3

3,234 people with raised blood sugar, against placebo, mean 2.8 years

DPP trial3
Metformin -31%
Lifestyle programme -58%

Cases per 100 person-years: 11.0 on placebo, 7.8 on metformin, 4.8 with the lifestyle programme. To prevent one case in three years it took 13.9 people on metformin or 6.9 in the lifestyle programme.

Less muscle gain during training5

94 people aged 65 and over, 14 weeks of strength training, gain from baseline

Lean mass (DXA)5
Placebo 1.95%
Metformin 0.41%
Thigh muscle mass (DXA)5
Placebo 3.90%
Metformin 0.45%
Thigh muscle area (CT)5
Placebo 6.43%
Metformin 2.27%

Values from the full text. Knee extension strength rose by 23.1 percent on placebo and 15.3 percent on metformin, this difference was not statistically certain. Body fat fell equally in both groups.

Frosted glass model of a liver on a clear glass block, next to it a single sugar cube, on a white pedestal in a bright room
The large trials measured diabetes cases, heart attacks and deaths, not just blood sugar. Symbolic image.

Research status

Where the research stands

Metformin has been approved in the US since 1995. On ClinicalTrials.gov 3,132 trials list metformin among their interventions, often as background or comparator. Shown are registered trials on diabetes prevention, ageing and training. UKPDS is not listed there. As of 26 Oct 2026. 9

  1. Preclinical Principle according to ChEMBL: inhibition of complex I in the mitochondria
  2. Phase 1 1 trial, 1 completed
  3. Phase 2 1 trial, 1 completed
  4. Phase 3 4 trials, 4 completed
  5. Approval in the US since 1995
6,293 participants in phase 3 Approved: Drugs@FDA lists the first US approval on 3 March 1995, ChEMBL lists metformin with phase 4 as the highest phase.8
Show all 7 phase 2, 3 and 4 trials on a timelineHide timeline 6 completed 1 running 2 with results
Phase 2
Phase 3
Phase 4

Bar: start to primary endpoint (planned for running trials). Green = completed, blue = progress until 26 Oct 2026. Phase 1: 1 trial on safety and pharmacokinetics, not shown as bars.

Side effects

  • Gut complaints: diarrhoea, nausea, bloating. For most people dose-dependent and temporary if titrated slowly and taken with food.
  • Vitamin B12 deficiency: measurable with use over months. Needs checking.
  • Blunted training adaptation: smaller strength and muscle gains. The mechanism, not a side effect in the narrower sense.
  • Lactic acidosis: very rare, but the classic warning. Relevant with impaired kidney function, severe illness, or before investigations with iodine contrast media, where it is paused beforehand.
  • Metallic taste: harmless, but commonly reported.

Tolerability

Side effects compared with placebo

The gut is the limiting factor, vitamin B12 drops over the years.

12 of 100 Placebo
53 of 100 Metformin
Event PlaceboMetformin
Diarrhoea7 12%53%
Nausea or vomiting7 8%26%
Flatulence7 6%12%
Indigestion7 4%7%
B12 low or borderline (5 years)6 10%19%

Diarrhoea led 6 percent to stop. According to the label lactic acidosis is very rare but dangerous, above all with impaired kidney function.7

Storage

Store dry, at room temperature and protected from light. Keep out of reach of children.

Three white tablet bottles on a bright shelf next to a folded light blue towel
Dry, at room temperature and away from light. Symbolic image.

Related

Related compounds

Same targets or a different path: all in the TPD lexicon.

Metformin (Glucophage)
AICAR Activates AMPK directly, data almost only from animal models Jardiance (Empagliflozin) Different path, sugar leaves the body via the urine Semaglutide Different path, GLP-1 receptor instead of the liver Lantus (Insulin Glargine) Basal insulin, together with metformin the risk of low blood sugar rises MOTS-c Mitochondrial peptide, metabolism and insulin sensitivity Atorvastatin (Lipitor) Different path, blood lipids instead of blood sugar

FAQ

Common questions about Metformin (Glucophage)

Short answers, each backed by the sources below.

How does metformin lower blood sugar?

According to the label it lowers glucose production in the liver, slows glucose uptake in the gut and improves uptake into muscle and tissue. Insulin secretion stays the same. ChEMBL lists complex I and glycerol-3-phosphate dehydrogenase in the mitochondria as direct targets. The plasma half-life is about 6.2 hours.710

Is metformin approved?

Yes. Drugs@FDA lists the first US approval on 3 March 1995, ChEMBL lists metformin as an approved compound. On ClinicalTrials.gov 3,132 trials list metformin among their interventions (as of 26 October 2026). Everything here is the state of research, not a recommendation.8109

What did UKPDS show?

In UKPDS 34, 753 overweight people with new type 2 diabetes received metformin or diet alone for a median of 10.7 years. Diabetes-related endpoints fell by 32 percent, diabetes-related deaths by 42 percent, all-cause mortality by 36 percent. In a supplementary trial, early addition to sulphonylureas was instead linked to more diabetes-related deaths. Ten years after the trial ended (UKPDS 80) heart attacks were still 33 percent lower and deaths 27 percent lower.12

What did DPP show in prediabetes?

3,234 people with raised blood sugar received placebo, metformin or a lifestyle programme aiming for at least 7 percent weight loss and 150 minutes of activity per week. After a mean of 2.8 years the rate of new diabetes was 11.0, 7.8 and 4.8 per 100 person-years. Metformin cut it by 31 percent, lifestyle by 58 percent and was clearly more effective.3

Does metformin blunt muscle growth?

In MASTERS 94 people aged 65 and over did 14 weeks of strength training on metformin or placebo. On placebo lean mass rose by 1.95 percent, on metformin by 0.41 percent, thigh muscle mass by 3.90 versus 0.45 percent. For strength there was only a trend. In the muscle samples AMPK was more active, the mTOR rise tended to be weaker. Whether younger people react the same, the trial does not show.5

What about vitamin B12?

In the DPP follow-up after 5 years 4.3 percent on metformin had a low B12 value, 2.3 percent on placebo. Low or borderline were 19.1 versus 9.5 percent, after 13 years 20.3 versus 15.6 percent. Every year of use raised the odds of a deficiency. The label reports about 7 percent with newly lowered B12 in 29-week trials.67

Does metformin extend life?

That is not proven. The 2014 observational study compared 78,241 people with type 2 diabetes who started on metformin with 90,463 matched people without diabetes. Adjusted median survival in the comparison group was 15 percent lower. An observational study is not proof of efficacy though. The registered ageing trials are small.49

Glossary

Terms explained briefly

Dotted words in the text open these explanations directly.

AMPK
The cell's energy sensor. It switches on when energy is short and turns to saving.
Biguanide
The compound class metformin belongs to. It lowers blood sugar without driving insulin secretion.
Complex I
First building block of the respiratory chain in the mitochondria. If it is slowed, the cell's energy yield drops.
HbA1c
Share of haemoglobin with sugar attached. Reflects blood sugar over the last two to three months.
Insulin sensitivity
How well cells respond to insulin and take up sugar from the blood.
Lactic acidosis
Acidification of the blood by lactic acid. Very rare but dangerous, above all with weak kidneys.
Lean mass
Body weight without fat, mainly muscle, organs and water.
Legacy effect
An advantage from the trial period that is still measurable years later, although the values have converged.
mTOR
Switch point for growth. With plenty of energy and amino acids it drives protein building.
Observational study
Analysis of existing data without random allocation. It shows associations, not cause.
Prediabetes
Blood sugar above the normal range but still below the diabetes threshold.

Evidence

Sources

Show all 10 sourcesHide sources 6 Studies1 Trial registry3 Database checked 26 Oct 2026

Studies

  1. UKPDS 34: metformin in overweight people with type 2 diabetes

    UK Prospective Diabetes Study (UKPDS) Group, The Lancet, 1998

    DOI 10.1016/S0140-6736(98)07037-8 PMID 9742977
    Checked 26 Oct 2026 via doi.org, Crossref, PubMed
  2. UKPDS 80: ten-year follow-up, legacy effect

    Holman et al., New England Journal of Medicine, 2008

    DOI 10.1056/NEJMoa0806470 PMID 18784090
    Checked 26 Oct 2026 via doi.org, Crossref, PubMed
  3. DPP: lifestyle or metformin for diabetes prevention

    Knowler et al. (Diabetes Prevention Program Research Group), New England Journal of Medicine, 2002

    DOI 10.1056/NEJMoa012512 PMID 11832527 NCT00004992
    Checked 26 Oct 2026 via doi.org, Crossref, PubMed
  4. Survival on metformin compared with people without diabetes (observational study)

    Bannister et al., Diabetes, Obesity and Metabolism, 2014

    DOI 10.1111/dom.12354 PMID 25041462
    Checked 26 Oct 2026 via doi.org, Crossref, PubMed
  5. MASTERS: metformin blunts muscle gain during strength training

    Walton et al., Aging Cell, 2019

    DOI 10.1111/acel.13039 PMID 31557380 NCT02308228
    Checked 26 Oct 2026 via doi.org, Crossref, PubMed, PubMed Central
  6. Vitamin B12 with long-term metformin use (DPP follow-up)

    Aroda et al., Journal of Clinical Endocrinology and Metabolism, 2016

    DOI 10.1210/jc.2015-3754 PMID 26900641 NCT00038727
    Checked 26 Oct 2026 via doi.org, Crossref, PubMed

Trial registry

  1. Trials on metformin on ClinicalTrials.gov

    ClinicalTrials.gov, U.S. National Library of Medicine

    Checked 26 Oct 2026 via ClinicalTrials.gov API v2

Database

  1. US prescribing information for metformin tablets

    DailyMed, U.S. National Library of Medicine (Stand 16.04.2026)

    Checked 26 Oct 2026 via DailyMed, openFDA
  2. First approval in Drugs@FDA

    Drugs@FDA, U.S. Food and Drug Administration (NDA 020357, Zulassung 03.03.1995)

    Checked 26 Oct 2026 via openFDA
  3. Mechanism and approval in ChEMBL

    ChEMBL, EMBL-EBI (CHEMBL1431, Mechanismus am Hydrochlorid CHEMBL1703)

    Checked 26 Oct 2026 via ChEMBL, UniProt