At a glance
Effects
- Blood-glucose lowering: Reduces fasting blood glucose by suppressing excess hepatic gluconeogenesis and enhancing peripheral glucose uptake; lowers HbA1c by approximately 2% [1].
- Insulin sensitisation: Improves cellular response to available insulin in muscle and adipose tissue without raising insulin secretion, reducing hyperinsulinaemia [4].
- Lipid improvement: Reduces serum triglycerides by 15–20% and may modestly lower LDL cholesterol without significant effect on HDL [7].
- Weight neutrality: Unlike sulphonylureas or insulin, metformin does not promote weight gain and is often associated with modest weight loss [6].
- Cardiovascular protection: Metformin is the only oral antidiabetic agent shown in landmark trials to reduce cardiovascular events in type 2 diabetes [7].
- No hypoglycaemia (monotherapy): Does not cause hypoglycaemia as monotherapy because it does not raise insulin levels; risk only arises when combined with insulin or insulin secretagogues [6].
Biguanide antihyperglycaemic
~6.2 h plasma; ~17.6 h in blood (erythrocyte compartment)
Oral (tablet or extended-release capsule)
Peak plasma ~1–2 h; glucose-lowering effect within days of starting
Renal excretion unchanged; ~90% within 24 h; not hepatically metabolised
About Metformin
Every point here is drawn from public medical and harm-reduction sources. A bracketed number after a claim — like [1]— is a reference: tap it to open the exact source it's based on (numbered list at the bottom). It is not a rating or score. Educational information, not medical advice.
Product specifics
- Est. delivery
- 3–7 business days · EU tracked
Product details as stated by the vendor (claims, not independently verified). Delivery is our standard EU estimate.
What it is
How it works
Metformin works through several complementary pathways. Its primary action is suppression of hepatic gluconeogenesis — the liver's overproduction of glucose — partly by inhibiting mitochondrial complex I and mitochondrial glycerophosphate dehydrogenase (mGPDH), which raises cellular AMP levels [3]. This energy stress activates AMP-activated protein kinase (AMPK), a master metabolic switch that further dampens glucose output and improves insulin sensitivity in muscle and fat tissue [4]. It also slows intestinal glucose absorption and may favourably remodel the gut microbiota [5]. Crucially, metformin does not stimulate insulin secretion from the pancreas, so it carries a very low intrinsic risk of hypoglycaemia when used alone [6].
Risks & side effects
Most important: The most serious risk is metformin-associated lactic acidosis (MALA) — a rare but potentially fatal build-up of lactic acid, reported at approximately 3 cases per 100,000 patient-years, with mortality historically reported as high as 50% in confirmed cases [8]. Risk is concentrated in patients with renal impairment, hepatic disease, hypoxic states, or excessive alcohol use, and is greatly reduced by respecting contraindications [9].
Common
Serious
- Metformin-associated lactic acidosis (MALA): rare (~3/100,000 patient-years) but life-threatening; symptoms include malaise, myalgias, respiratory distress, somnolence, and abdominal pain [8]
- Vitamin B12 deficiency leading to peripheral neuropathy or megaloblastic anaemia if uncorrected over years [12]
- Accumulation and toxicity in acute kidney injury or worsening renal function [9]
Safety & harm reduction
- Significant renal impairment (eGFR <30 mL/min/1.73 m²; use with extreme caution at eGFR 30–45) [9]
- Chronic hepatic disease (increased MALA risk) [9]
- Acute or chronic metabolic acidosis, including diabetic ketoacidosis [13]
- Known hypersensitivity to metformin hydrochloride [13]
- Congestive heart failure requiring pharmacological treatment [14]
- Conditions associated with hypoxia: acute MI, pulmonary insufficiency, septicaemia [9]
- Excessive alcohol intake (additive lactic acidosis risk) [9]
- Patients undergoing iodinated contrast imaging or surgery (withhold peri-procedure) [2]
- Renal function (serum creatinine / eGFR): before initiation and at least annually thereafter [2]
- Serum vitamin B12 and haematological parameters: annually in long-term users [2]
- Blood glucose and HbA1c: periodically to assess glycaemic control [1]
- Serum lactate if symptoms of lactic acidosis arise (malaise, myalgia, respiratory distress) [8]
- Carbonic anhydrase inhibitors (topiramate, acetazolamide, zonisamide): additive metabolic acidosis risk [2]
- Cationic drugs excreted by renal tubular secretion (digoxin, morphine, vancomycin, trimethoprim, quinidine): compete for renal clearance, potentially raising metformin levels [13]
- Furosemide: raises metformin Cmax by ~22% [13]
- Iodinated contrast agents: risk of acute kidney injury causing metformin accumulation; withhold before and 48 h after [2]
- Alcohol: potentiates lactic acidosis risk; avoid excessive intake [2]
- Insulin / insulin secretagogues (sulphonylureas): increased hypoglycaemia risk [6]
- Acid-suppressing drugs (PPIs / H2 blockers): additive vitamin B12 depletion risk [15]
- Take with food to minimise gastrointestinal side effects [10]
- Start at low dose (e.g. 500 mg once or twice daily) and titrate slowly over 2–4 weeks to reduce GI side effects [10]
- Supplement vitamin B12 (or monitor annually) in long-term users, especially at higher doses [15]
- Withhold before elective procedures requiring contrast dye or prolonged fasting [2]
- Restart only after confirming adequate renal function post-procedure [2]
Dosage context
Commonly reported therapeutic dosage range is 500 mg to 3,000 mg per day (immediate-release), typically divided into 2–3 doses with meals [16]. The maximum effective dose is generally cited as 2,500 mg/day, with the approved maximum at 3,000 mg/day for immediate-release formulations. Extended-release (XR) formulations: standard range 500–2,000 mg once daily [16]. These are medical prescribing ranges — not a personal recommendation. Dose must be individualised by a clinician based on renal function and tolerability. Caution is needed when exceeding 1,700 mg/day in the elderly or those with any renal impairment [9].
Sources
- 1.ClinicalTrials.gov – Diabetes Prevention Program Outcomes Study Protocol
- 2.FDA Prescribing Information – Metformin HCl Extended-Release (accessdata.fda.gov)
- 3.Endocrine Reviews – Cellular and Molecular Mechanisms of Metformin Action (Oxford Academic)
- 4.PMC – Metformin in Therapeutic Applications (NCB)
- 5.PMC – Role of Mitochondria in Metformin Action
- 6.ClinicalTrials.gov – Metformin as Upstream Therapy in Atrial Fibrillation
- 7.ClinicalTrials.gov – Metformin/Gliclazide Bioequivalence Study (Pharmacological Properties)
- 8.PMC – Metformin-Associated Lactic Acidosis: Case Report and Review (Cureus 2022)
- 9.Medsafe NZ – Metformin and Fatal Lactic Acidosis
- 10.ClinicalTrials.gov – Atrial Fibrillation Metformin Protocol (adverse reactions)
- 11.ClinicalTrials.gov – Metformin/Gliclazide Food Effect Study (adverse reactions)
- 12.GoodRx – Metformin and Vitamin B12
- 13.ClinicalTrials.gov – Endometrial Cancer Chemoprevention Study (contraindications & interactions)
- 14.ClinicalTrials.gov – Endometrial Cancer Chemoprevention Study (Contraindications)
- 15.LiveHealthyRx – Vitamin B12 and Metformin
- 16.ClinicalTrials.gov – Copanlisib / Metformin Pharmacokinetics (dosage range)
This information is provided for educational and harm-reduction purposes only. It is not medical advice. These substances can carry serious health risks; effects and safe use vary by individual. Consult a qualified healthcare professional before use. Legal status varies by country — it is your responsibility to know your local law. We do not encourage misuse.