-
1.
Once-weekly tirzepatide versus once-daily insulin degludec as add-on to metformin with or without SGLT2 inhibitors in patients with type 2 diabetes (SURPASS-3): a randomised, open-label, parallel-group, phase 3 trial.
Ludvik, B, Giorgino, F, Jódar, E, Frias, JP, Fernández Landó, L, Brown, K, Bray, R, Rodríguez, Á
Lancet (London, England). 2021;(10300):583-598
Abstract
BACKGROUND Tirzepatide is a novel dual glucose-dependent insulinotropic polypeptide and GLP-1 receptor agonist under development for the treatment of type 2 diabetes. We aimed to assess the efficacy and safety of tirzepatide versus titrated insulin degludec in people with type 2 diabetes inadequately controlled by metformin with or without SGLT2 inhibitors. METHODS In this open-label, parallel-group, multicentre (122 sites), multinational (13 countries), phase 3 study, eligible participants (aged ≥18 years) had a baseline glycated haemoglobin (HbA1c) of 7·0-10·5%, body-mass index of at least 25 kg/m2, stable weight, and were insulin-naive and treated with metformin alone or in combination with an SGLT2 inhibitor for at least 3 months before screening. Participants were randomly assigned (1:1:1:1), using an interactive web-response system, to once-weekly subcutaneous injection of tirzepatide (5, 10, or 15 mg) or once-daily subcutaneous injection of titrated insulin degludec, and were stratified by country, HbA1c, and concomitant use of oral antihyperglycaemic medications. Tirzepatide was initially given at 2·5 mg and the dose was escalated by 2·5 mg every 4 weeks until the assigned dose was reached. Insulin degludec was initially given at 10 U per day and was titrated once weekly to a fasting self-monitored blood glucose of less than 5·0 mmol/L (<90 mg/dL), following a treat-to-target algorithm, for 52 weeks. The primary efficacy endpoint was non-inferiority of tirzepatide 10 mg or 15 mg, or both, versus insulin degludec in mean change from baseline in HbA1c at week 52. Key secondary efficacy endpoints were non-inferiority of tirzepatide 5 mg versus insulin degludec in mean change from baseline in HbA1c at week 52, superiority of all doses of tirzepatide versus insulin degludec in mean change from baseline in HbA1c and bodyweight, and the proportion of participants achieving HbA1c of less than 7·0% (<53 mmol/mol) at week 52. We used a boundary of 0·3% to establish non-inferiority in HbA1c difference between treatments. Efficacy and safety analyses were assessed in the modified intention-to-treat population (all participants who received at least one dose of study drug). This trial is registered with ClinicalTrials.gov, number NCT03882970, and is complete. FINDINGS Between April 1 and Nov 15, 2019, we assessed 1947 participants for eligibility, 1444 of whom were randomly assigned to treatment. The modified intention-to-treat population was 1437 participants from the tirzepatide 5 mg (n=358), tirzepatide 10 mg (n=360), tirzepatide 15 mg (n=359), and insulin degludec (n=360) groups. From a mean baseline HbA1c of 8·17% (SD 0·91), the reductions in HbA1c at week 52 were 1·93% (SE 0·05) for tirzepatide 5 mg, 2·20% (0·05) for tirzepatide 10 mg, and 2·37% (0·05) for tirzepatide 15 mg, and 1·34% (0·05) for insulin degludec. The non-inferiority margin of 0·3% was met. The estimated treatment difference (ETD) versus insulin degludec ranged from -0·59% to -1·04% for tirzepatide (p<0·0001 for all tirzepatide doses). The proportion of participants achieving a HbA1c of less than 7·0% (<53 mmol/mol) at week 52 was greater (p<0·0001) in all three tirzepatide groups (82%-93%) versus insulin degludec (61%). At week 52, from a baseline of 94·3 kg (SD 20·1), all three tirzepatide doses decreased bodyweight (-7·5 kg to -12·9 kg), whereas insulin degludec increased bodyweight by 2·3 kg. The ETD versus insulin degludec ranged from -9·8 kg to -15·2 kg for tirzepatide (p<0·0001 for all tirzepatide doses). The most common adverse events in tirzepatide-treated participants were mild to moderate gastrointestinal events that decreased over time. A higher incidence of nausea (12-24%), diarrhoea (15-17%), decreased appetite (6-12%), and vomiting (6-10%) was reported in participants treated with tirzepatide than in those treated with insulin degludec (2%, 4%, 1%, and 1%, respectively). Hypoglycaemia (<54 mg/dL or severe) was reported in five (1%), four (1%), and eight (2%) participants on tirzepatide 5, 10, and 15 mg, respectively, versus 26 (7%) on insulin degludec. Treatment discontinuation due to an adverse event was more common in the tirzepatide groups than in the insulin degludec group. Five participants died during the study; none of the deaths were considered by the investigators to be related to the study treatment. INTERPRETATION In patients with type 2 diabetes, tirzepatide (5, 10, and 15 mg) was superior to titrated insulin degludec, with greater reductions in HbA1c and bodyweight at week 52 and a lower risk of hypoglycaemia. Tirzepatide showed a similar safety profile to that of GLP-1 receptor agonists. FUNDING Eli Lilly and Company.
-
2.
Cancer Antigen 15-3/Mucin 1 Levels in CCTG MA.32: A Breast Cancer Randomized Trial of Metformin vs Placebo.
Goodwin, PJ, Dowling, RJO, Ennis, M, Chen, BE, Parulekar, WR, Shepherd, LE, Gelmon, KA, Whelan, TJ, Ligibel, JA, Hershman, DL, et al
JNCI cancer spectrum. 2021;(5)
Abstract
BACKGROUND Circulating levels of cancer antigen (CA) 15-3, a tumor marker and regulator of cellular metabolism, were reduced by metformin in a nonrandomized neoadjuvant study. We examined the effects of metformin (vs placebo) on CA 15-3 in participants of MA.32, a phase III randomized trial in early-stage breast cancer. METHODS A total of 3649 patients with T1-3, N0-3, M0 breast cancer were randomly assigned; pretreatment and 6-month on-treatment fasting plasma were centrally assayed for CA 15-3. Genomic DNA was analyzed for the rs11212617 single nucleotide polymorphism. Absolute and relative change of CA 15-3 (metformin vs placebo) were compared using Wilcoxon rank and t tests. Regression models adjusted for baseline differences and assessed key interactions. All statistical tests were 2-sided. RESULTS Mean (SD) age was 52.4 (10.0) years. The majority of patients had T2/3, node-positive, hormone receptor-positive, HER2-negative breast cancer treated with (neo)adjuvant chemotherapy and hormone therapy. Mean (SD) baseline CA 15-3 was 17.7 (7.6) and 18.0 (8.1 U/mL). At 6 months, CA 15-3 was statistically significantly reduced in metformin vs placebo arms (absolute geometric mean reduction in CA 15-3 = 7.7% vs 2.0%, P < .001; relative metformin: placebo level of CA 15-3 [adjusted for age, baseline body mass index, and baseline CA 15-3] = 0.94, 95% confidence interval = 0.92 to 0.96). This reduction was independent of tumor characteristics, perioperative systemic therapy, baseline body mass index, insulin, and the single nucleotide polymorphism status (all Ps > .11). CONCLUSIONS Our observation that metformin reduces CA 15-3 by approximately 6% was corroborated in a large placebo-controlled randomized trial. The clinical implications of this reduction in CA 15-3 will be explored in upcoming efficacy analyses of breast cancer outcomes in MA.32.
-
3.
Metformin for gestational diabetes study: metformin vs insulin in gestational diabetes: glycemic control and obstetrical and perinatal outcomes: randomized prospective trial.
Picón-César, MJ, Molina-Vega, M, Suárez-Arana, M, González-Mesa, E, Sola-Moyano, AP, Roldan-López, R, Romero-Narbona, F, Olveira, G, Tinahones, FJ, González-Romero, S
American journal of obstetrics and gynecology. 2021;(5):517.e1-517.e17
Abstract
BACKGROUND Gestational diabetes that is not properly controlled with diet has been commonly treated with insulin. In recent years, several studies have published that metformin can lead to, at least, similar obstetrical and perinatal outcomes as insulin. Nevertheless, not all clinical guidelines endorse its use, and clinical practice is heterogeneous. OBJECTIVE This study aimed to test whether metformin could achieve the same glycemic control as insulin and similar obstetrical and perinatal results, with a good safety profile, in women with gestational diabetes that is not properly controlled with lifestyle changes. STUDY DESIGN The metformin for gestational diabetes study was a multicenter, open-label, parallel arms, randomized clinical trial performed at 2 hospitals in Málaga (Spain), enrolling women with gestational diabetes who needed pharmacologic treatment. Women at the age of 18 to 45 years, in the second or third trimesters of pregnancy, were randomized to receive metformin or insulin (detemir or aspart). The main outcomes were (1) glycemic control (mean glycemia, preprandial and postprandial) and hypoglycemic episodes and (2) obstetrical and perinatal outcomes and complications (hypertensive disorders, type of labor, prematurity, macrosomia, large for gestational age, neonatal care unit admissions, respiratory distress syndrome, hypoglycemia, jaundice). Outcomes were analyzed on an intention-to-treat basis. RESULTS Between October 2016 and June 2019, 200 women were randomized, 100 to the insulin-treated group and 100 to the metformin-treated group. Mean fasting and postprandial glycemia did not differ between groups, but postprandial glycemia was significantly better after lunch or dinner in the metformin-treated-group. Hypoglycemic episodes were significantly more common in the insulin-treated group (55.9% vs 17.7% on metformin; odds ratio, 6.118; 95% confidence interval, 3.134-11.944; P=.000). Women treated with metformin gained less weight from the enrollment to the prepartum visit (36-37 gestational weeks) (1.35±3.21 vs 3.87±3.50 kg; P=.000). Labor inductions (45.7% [metformin] vs 62.5% [insulin]; odds ratio, 0.506; 95% confidence interval, 0.283-0.903; P=.029) and cesarean deliveries (27.6% [metformin] vs 52.6% [insulin]; odds ratio, 0.345; 95% confidence interval, 0.187-0.625; P=.001) were significantly lower in the metformin-treated group. Mean birthweight, macrosomia, and large for gestational age and babies' complications were not different between treatment groups. The lower cesarean delivery rate for women treated with metformin was not associated with macrosomia, large or small for gestational age, or other complications of pregnancy. CONCLUSION Metformin treatment was associated with a better postprandial glycemic control than insulin for some meals, a lower risk of hypoglycemic episodes, less maternal weight gain, and a low rate of failure as an isolated treatment. Most obstetrical and perinatal outcomes were similar between groups.
-
4.
Metformin use is associated with a reduced risk of mortality in patients with diabetes hospitalised for COVID-19.
Lalau, JD, Al-Salameh, A, Hadjadj, S, Goronflot, T, Wiernsperger, N, Pichelin, M, Allix, I, Amadou, C, Bourron, O, Duriez, T, et al
Diabetes & metabolism. 2021;(5):101216
-
-
Free full text
-
Abstract
AIMS: Metformin exerts anti-inflammatory and immunosuppressive effects. We addressed the impact of prior metformin use on prognosis in patients with type 2 diabetes hospitalised for COVID-19. METHODS CORONADO is a nationwide observational study that included patients with diabetes hospitalised for COVID-19 between March 10 and April 10, 2020 in 68 French centres. The primary outcome combined tracheal intubation and/or death within 7 days of admission. A Kaplan-Meier survival curve was reported for death up to day 28. The association between metformin use and outcomes was then estimated in a logistic regression analysis after applying a propensity score inverse probability of treatment weighting approach. RESULTS Among the 2449 patients included, 1496 were metformin users and 953 were not. Compared with non-users, metformin users were younger with a lower prevalence of diabetic complications, but had more severe features of COVID-19 on admission. The primary endpoint occurred in 28.0% of metformin users (vs 29.0% in non-users, P = 0.6134) on day 7 and in 32.6% (vs 38.7%, P = 0.0023) on day 28. The mortality rate was lower in metformin users on day 7 (8.2 vs 16.1%, P < 0.0001) and on day 28 (16.0 vs 28.6%, P < 0.0001). After propensity score weighting was applied, the odds ratios for primary outcome and death (OR [95%CI], metformin users vs non-users) were 0.838 [0.649-1.082] and 0.688 [0.470-1.007] on day 7, then 0.783 [0.615-0.996] and 0.710 [0.537-0.938] on day 28, respectively. CONCLUSION Metformin use appeared to be associated with a lower risk of death in patients with diabetes hospitalised for COVID-19.
-
5.
Evaluation of the gut microbiota after metformin intervention in children with obesity: A metagenomic study of a randomized controlled trial.
Pastor-Villaescusa, B, Plaza-Díaz, J, Egea-Zorrilla, A, Leis, R, Bueno, G, Hoyos, R, Vázquez-Cobela, R, Latorre, M, Cañete, MD, Caballero-Villarraso, J, et al
Biomedicine & pharmacotherapy = Biomedecine & pharmacotherapie. 2021;:111117
Abstract
BACKGROUND Metformin, a first-line oral antidiabetic agent that has shown promising results in terms of treating childhood and adolescent obesity, might influence the composition of the gut microbiota. We aimed to evaluate whether the gut microbiota of non-diabetic children with obesity changes after a metformin intervention. METHODS The study was a multicenter and double-blind randomized controlled trial in 160 children with obesity. Children were randomly assigned to receive either metformin (1 g/day) or placebo for 6 months in combination with healthy lifestyle recommendations in both groups. Then, we conducted a metagenomic analysis in a subsample obtained from 33 children (15 metformin, 18 placebo). A linear mixed-effects model (LMM) was used to determine the abundance changes from baseline to six months according to treatment. To analyze the data by clusters, a principal component analysis was performed to understand whether lifestyle habits have a different influence on the microbiota depending on the treatment group. RESULTS Actinobacteria abundance was higher after placebo treatment compared with metformin. However, the interaction time x treatment just showed a trend to be significant (4.6% to 8.1% after placebo vs. 3.8 % to 2.6 % after metformin treatment, p = 0.055). At genus level, only the abundance of Bacillus was significantly higher after the placebo intervention compared with metformin (2.5% to 5.7% after placebo vs. 1.5 % to 0.8 % after metformin treatment, p = 0.044). Furthermore, different ensembles formed by Firmicutes, Bacteroidetes, and Verrucomicrobia were found according to the interventions under a similar food consumption. CONCLUSION Further studies with a large sample size controlled by lifestyle patterns are required in obese children and adolescents to clarify whether metformin might trigger gut microbiota alterations. TRIAL REGISTRATION Registered on the European Clinical Trials Database (EudraCT, ID: 2010-023061-21) on 14 November 2011.
-
6.
Insulin resistance in type 1 diabetes managed with metformin (INTIMET): Study protocol of a double-blind placebo-controlled, randomised trial.
Snaith, JR, Samocha-Bonet, D, Evans, J, Liu, Z, Kowalski, G, Bruce, C, Holmes-Walker, DJ, Greenfield, JR
Diabetic medicine : a journal of the British Diabetic Association. 2021;(9):e14564
Abstract
BACKGROUND Insulin resistance is an under-recognised metabolic defect and cardiovascular risk factor in Type 1 diabetes. Whether metformin improves hepatic, muscle or adipose tissue insulin sensitivity has not been studied in adults with Type 1 diabetes. We initiated the INTIMET study (INsulin resistance in Type 1 diabetes managed with METformin), a double-blind randomised, placebo-controlled trial to measure the effect of metformin on tissue-specific insulin resistance in adults with Type 1 diabetes. METHODS We will study 40 adults aged 20-55 years with Type 1 diabetes (HbA1c ≤ 80 mmol/mol [9.5%], fasting C-peptide <0.3 nmol/L) and 20 age-, gender- and body mass index (BMI)-matched controls. Insulin sensitivity will be determined by the two-step hyperinsulinaemic-euglycaemic clamp method with deuterated glucose to document liver, muscle and adipose insulin sensitivity. Subjects with Type 1 diabetes will be randomised to metformin extended-release 1500 mg daily or matched placebo for 26 weeks. The primary outcome is change in hepatic insulin sensitivity, assessed by change in basal rate of appearance (Ra) of glucose and suppression of endogenous glucose production (EGP) during the low-dose stage of the clamp. CONCLUSION The INTIMET study is the first clinical trial to quantify the impact of metformin on liver, muscle and adipose insulin resistance in adults with Type 1 diabetes. This study may identify factors that predict an individual's response to metformin in Type 1 diabetes. TRIAL REGISTRATION ACTRN12619001440112.
-
7.
Withdrawal of medications leads to worsening of OGTT parameters in youth with impaired glucose tolerance or recently-diagnosed type 2 diabetes.
Hannon, TS, Edelstein, SL, Arslanian, SA, Caprio, S, Zeitler, PS, Buchanan, TA, Ehrmann, DA, Mather, KJ, Tripputi, M, Kahn, SE, et al
Pediatric diabetes. 2020;(8):1437-1446
-
-
Free full text
-
Abstract
BACKGROUND The RISE Pediatric Medication Study compared strategies for preserving β-cell function, including a 9-month follow-up after treatment withdrawal to test treatment effect durability. OBJECTIVE Evaluate OGTT measures of glucose and β-cell response through 12 months of intervention and 9 months of medication washout. PARTICIPANTS Youth (n = 91) aged 10 to 19 years with BMI ≥85th percentile and impaired glucose tolerance (IGT) or recently diagnosed type 2 diabetes (T2D). METHODS A multicenter randomized clinical trial comparing insulin glargine for 3 months followed by metformin for 9 months (G→Met) or metformin alone (Met) for 12 months. We report within-group changes from baseline to end of medication intervention (M12), baseline to 9 months post-medication withdrawal (M21), and end of medication (M12) to M21. OGTT C-peptide index [CPI] paired with 1/fasting insulin evaluated β-cell response. RESULTS At M12, both treatments were associated with stable fasting glucose (G→Met baseline 6.0 ± 0.1 vs M12 5.9 ± 0.2 mmol/L, P = .62; Met baseline 6.1 ± 0.2 vs M12 6.0 ± 0.2 mmol/L, P = .73) and 2-hour glucose (G→Met baseline 10.2 ± 0.4 vs M12 9.3 ± 0.5 mmol/L, P = .03; Met baseline 10.2 ± 0.4 vs M12 10.6 ± 0.6 mmol/L, P = .88). Following medication withdrawal, fasting glucose worsened (G→Met M21 8.6 ± 1.8, P = .004; Met M21 7.8 ± 0.7 mmol/L, P = .003), as did 2-hour glucose (G→Met M21 13.2 ± 1.4, P = .002; Met M21 13.1 ± 1.2 mmol/L, P = .006), associated with declines in β-cell response. CONCLUSIONS G→Met and Met were associated with stable glucose measures during 12 months of treatment in youth with IGT or recently diagnosed T2D. Glucose and β-cell response worsened post-medication withdrawal, suggesting treatment must be long-term or alternative treatments pursued.
-
8.
Efficacy and Safety of Pioglitazone versus Glimepiride after Metformin and Alogliptin Combination Therapy: A Randomized, Open-Label, Multicenter, Parallel-Controlled Study.
Kim, JM, Kim, SS, Kim, JH, Kim, MK, Kim, TN, Lee, SH, Lee, CW, Park, JY, Kim, ES, Lee, KJ, et al
Diabetes & metabolism journal. 2020;(1):67-77
Abstract
BACKGROUND There is limited information regarding the optimal third-line therapy for managing type 2 diabetes mellitus (T2DM) that is inadequately controlled using dual combination therapy. This study assessed the efficacy and safety of pioglitazone or glimepiride when added to metformin plus alogliptin treatment for T2DM. METHODS This multicenter, randomized, active-controlled trial (ClinicalTrials.gov: NCT02426294) recruited 135 Korean patients with T2DM that was inadequately controlled using metformin plus alogliptin. The patients were then randomized to also receive pioglitazone (15 mg/day) or glimepiride (2 mg/day) for a 26-week period, with dose titration was permitted based on the investigator's judgement. RESULTS Glycosylated hemoglobin levels exhibited similar significant decreases in both groups during the treatment period (pioglitazone: -0.81%, P<0.001; glimepiride: -1.05%, P<0.001). However, the pioglitazone-treated group exhibited significantly higher high density lipoprotein cholesterol levels (P<0.001) and significantly lower homeostatic model assessment of insulin resistance values (P<0.001). Relative to pioglitazone, adding glimepiride to metformin plus alogliptin markedly increased the risk of hypoglycemia (pioglitazone: 1/69 cases [1.45%], glimepiride: 14/66 cases [21.21%]; P<0.001). CONCLUSION Among patients with T2DM inadequately controlled using metformin plus alogliptin, the addition of pioglitazone provided comparable glycemic control and various benefits (improvements in lipid profiles, insulin resistance, and hypoglycemia risk) relative to the addition of glimepiride.
-
9.
N-ACETYLCYSTEINE AND/OR URSODEOXYCHOLIC ACID ASSOCIATED WITH METFORMIN IN NON-ALCOHOLIC STEATOHEPATITIS: AN OPEN-LABEL MULTICENTER RANDOMIZED CONTROLLED TRIAL.
Oliveira, CP, Cotrim, HP, Stefano, JT, Siqueira, ACG, Salgado, ALA, Parise, ER
Arquivos de gastroenterologia. 2019;(2):184-190
Abstract
BACKGROUND Nowadays, pharmacological treatment of non-alcoholic fatty liver disease (NAFLD) is still limited and it is based on the treatment of conditions associated comorbities. Oxidative stress and insulin resistance are the mechanisms that seem to be mostly involved in its pathogenesis. OBJECTIVE To evaluate the efficacy of N-acetylcysteine (NAC) in combination with metformin (MTF) and/or ursodeoxycholic acid (UDCA) for treatment of non-alcoholic steatohepatitis (NASH). METHODS Open-label multicenter randomized trial was conducted for 48 weeks. It included patients with biopsy-proven NASH. The patients were randomized into three groups: NAC (1.2 g) + UDCA (15 mg/kg) + MTF (850-1500 mg/day) (n=26); UDCA (20 mg/kg) + MTF (850-1500 mg/day) (n=13); NAC (1.2g) + MTF (850-1500 mg/day) (n=14) for 48 weeks. Clinical, laboratory and the second liver biopsies were performed after 48 weeks. RESULTS A total of 53 patients were evaluated; 17 (32.1%) were males; median age ±54 (IQR=15, 21-71) years. In the baseline, no difference was seen between groups according clinical and histological parameters. The groups differed only in cholesterol, LDL and triglycerides. No significant differences in biochemical and histologic parameters were found between these the three groups after 48 weeks of treatment. In the intragroup analysis (intention-to-treat) comparing histological and biochemical features, there were significant improvements in the steatosis degree (P=0.014), ballooning (0.027) and, consequently, in the NAFLD Activity Score (NAS) (P=0.005), and in the ALT levels at the end of the treatment only in the NAC + MTF group. No significant evidence of modification in the liver fibrosis could be observed in any of the groups. CONCLUSION This multicenter study suggests that the association of NAC + MTF could reduce the liver disease activity in patients with NASH. These data stimulate further controlled studies with this therapy for these patients.
-
10.
Effect of metformin in addition to dietary and lifestyle advice for pregnant women who are overweight or obese: the GRoW randomised, double-blind, placebo-controlled trial.
Dodd, JM, Louise, J, Deussen, AR, Grivell, RM, Dekker, G, McPhee, AJ, Hague, W
The lancet. Diabetes & endocrinology. 2019;(1):15-24
Abstract
BACKGROUND Maternal overweight and obesity are associated with well recognised pregnancy complications. Antenatal dietary and lifestyle interventions have a modest effect on gestational weight gain without affecting pregnancy outcomes. We aimed to assess the effects on maternal and infant outcomes of antenatal metformin given in addition to dietary and lifestyle advice among overweight and obese pregnant women. METHODS GRoW was a multicentre, randomised, double-blind, placebo-controlled trial in which pregnant women at 10-20 weeks' gestation with a BMI of 25 kg/m2 or higher were recruited from three public maternity units in Adelaide, SA, Australia. Women were randomly assigned (1:1) via a computer-generated schedule to receive either metformin (to a maximum dose of 2000 mg per day) or matching placebo. Participants, their antenatal care providers, and research staff (including outcome assessors) were masked to treatment allocation. All women received an antenatal dietary and lifestyle intervention. The primary outcome was the proportion of infants with birthweight greater than 4000 g. Secondary outcomes included measures of maternal weight gain, maternal diet and physical activity, maternal pregnancy and birth outcomes, maternal quality of life and emotional wellbeing, and infant birth outcomes. Outcomes were analysed on an intention-to-treat basis (including all randomly assigned women who did not withdraw consent to use their data, and who did not have a miscarriage or termination of pregnancy before 20 weeks' gestation, or a stillbirth). The trial is registered with the Australian New Zealand Clinical Trials Registry, number ACTRN12612001277831. FINDINGS Of 524 women who were randomly assigned between May, 28 2013 and April 26, 2016, 514 were included in outcome analyses (256 in the metformin group and 258 in the placebo group). Median gestational age at trial entry was 16·29 weeks (IQR 14·43-18·00) and median BMI was 32·32 kg/m2 (28·90-37·10); 167 (32%) participants were overweight and 347 (68%) were obese. There was no significant difference in the proportion of infants with birthweight greater than 4000 g (40 [16%] with metformin vs 37 [14%] with placebo; adjusted risk ratio [aRR] 0·97, 95% CI 0·65 to 1·47; p=0·899). Women receiving metformin had lower average weekly gestational weight gain (adjusted mean difference -0·08 kg, 95% CI -0·14 to -0·02; p=0·007) and were more likely to have gestational weight gain below recommendations (aRR 1·46, 95% CI 1·10 to 1·94; p=0·008). Total gestational weight gain, pregnancy and birth outcomes, maternal diet and physical activity, and maternal quality of life and emotional wellbeing did not differ significantly between groups. Similar numbers of women in both treatment groups (76% [159/208] in the metformin group and 73% [144/196] in the placebo group) reported side-effects including nausea, diarrhoea, and vomiting. Two stillbirths (placebo group) and one neonatal death (metformin group) occurred; none of the perinatal deaths were determined to be attributable to participation in the trial. INTERPRETATION For pregnant women who are overweight or obese, metformin given in addition to dietary and lifestyle advice initiated at 10-20 weeks' gestation does not improve pregnancy and birth outcomes. FUNDING Australian National Health and Medical Research Council.