Metabolic & Cardiometabolic
metformin decreases insulin resistance
Part of: 💊 metformin
📅 Last reviewed: 2026-07-15 ⓘ
Evidence ladder
How far up the ladder this claim has climbed. A high consensus on a low rung means "consistent so far," not "proven in people."
Top evidence so far: All trials, pooled (Meta-analysis)
How the studies fall
What the evidence shows
Metformin lowers insulin / insulin resistance in PCOS (vs COCP comparator). Well-established insulin-sensitizer effect.
The evidence (9)
| Source | Grade | Stance | Quality | Finding |
|---|---|---|---|---|
| Widén EI, Eriksson JG, Groop LC 1992 · Diabetes | RCT | supports | moderate | clamp: metformin raised insulin-stimulated glucose disposal 25% |
| Trzcinski M, Chudzicka-Strugala I, Kim K, Piekarski P, Spaczynski R, Zwoździak B, Banaszewska B, Pawelczyk L, Chang RJ, Duleba AJ 2026 · Endocr Connect | observational | mixed | low | Single-arm open-label pre-post (NCT03489668), PCOS women, n=49 analysed, metformin 1500 mg/day x 3 months, no control arm. Fasting insulin 16.7 -> 13.5 uU/mL (-3.15 +/- 1.25, P=0.02), but the Matsuda insulin sensitivity index moved slightly the wrong way, 3.50 -> 3.29 (NS), and fasting glucose was unchanged (NS). BMI fell 3.6% (P<0.0001), confounding the insulin change. Two-way on insulin resistance. |
| Farkhondeh T, Amirabadizadeh A, Aramjoo H, Llorens S, Roshanravan B, Saeedi F, Talebi M, Shakibaei M, Samarghandian S 2021 · Curr Oncol | meta-analysis | tested-null | low | Meta-analysis of nine RCTs in non-diabetic women with operable breast or endometrial cancer (not PCOS). For insulin resistance the pooled HOMA-IR effect, from only four trials with 681 patients, was SMD -0.17 (95% CI -0.52 to 0.19, p = 0.36, I2 67%): no significant reduction. Fasting insulin was also non-significant (SMD -0.87, CI -1.93 to 0.19, I2 98%); only fasting glucose fell, slightly (SMD -0.18). The authors conclude metformin did not significantly change insulin, glucose, HOMA-IR or BMI and that heterogeneity and bias prevent confirming or rejecting efficacy. The paper carries internal reporting errors (inconsistent arm counts, a CI-crossing Ki-67 estimate described as a decrease). Underpowered trend toward the claim (point estimate favours it, interval includes no effect): graded tested-null per CONVENTIONS §5 second clarification 2026-09-26. |
| Murtaza S, Murtaza F, Yasin MU, Shahid A, Shahid M, Rehan MMB, Ata F, Asghar MS, Eljack MMF 2026 · Endocrinology, diabetes & metabolism | meta-analysis | supports | moderate | MA, 4 RCTs n=187 (non-diabetic on glucocorticoids): HOMA-IR MD -0.53 (95% CI -0.97 to -0.08, sig) vs placebo; but fasting insulin MD -2.26 (95% CI -5.90 to 1.38, NS) |
| Sun J, Wang Y, Zhang X, He H 2019 · Medicine (Baltimore) | meta-analysis | contradicts | moderate | MA: metformin showed no significant improvement in insulin resistance vs placebo in overweight/obese youth |
| Pan D et al 2026 · Research Square | meta-analysis | supports | moderate | MA/meta-regression, 14 RCTs n=882 (women with PMOS/PCOS-like syndrome): vitamin D improved HOMA-IR & fasting insulin; combo with metformin produced greater IR improvement than vitamin D alone |
| Davis SR, Robinson PJ, Jane F, White S, Brown KA, Piessens S, Edwards A, McNeilage J, Woinarski J, Chipman M, Bell RJ 2018 · Clin Endocrinol (Oxf) | RCT | supports | moderate | Placebo-controlled RCT: metformin produced greater HOMA-IR reduction vs placebo in women on tamoxifen |
| Melin J, Forslund M, Alesi S, Piltonen T, Romualdi D, Spritzer PM, Tay CT, Pena A, Witchel SF, Mousa A, Teede H 2024 · J Clin Endocrinol Metab | meta-analysis | supports | moderate | Pooled across 36 RCTs (GRADE): metformin lowered fasting insulin −27.12 pmol/L and triglycerides −0.15 mmol/L vs COCP; combination superior to COCP on insulin resistance (+0.44). |
| Dolati A, Ahmadimoghaddam D, Zamanirafe M, Rezaie S, Khazaie S, Mehrpooya M, Doostizadeh M 2026 · Human psychopharmacology | RCT | mixed | low | RCT n=84, antipsychotic-induced weight gain: both empagliflozin & metformin(1000mg/d) improved glycemic/lipid params over 12wk; empagliflozin sig. greater HOMA-IR & fasting insulin reduction (p=0.012, p=0.005) than metformin |
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Educational only, not medical advice. Grades and scores reflect published evidence weighted by study design and quality; see the methodology.