Metformin was found to reduce the incidence of new-onset type 2 diabetes mellitus (T2DM) vs standard diet and exercise, but not compared with intensive diet and exercise, according to a new review published in the Cochrane Database of Systematic Reviews.
“Metformin compared with placebo or diet and exercise reduced or delayed the risk of T2DM in people at increased risk for the development of T2DM (moderate-quality evidence). However, metformin compared to intensive diet and exercise did not reduce or delay the risk of T2DM,” said researchers in their report.
Researchers reviewed 20 randomized controlled trials (RCTs) with a total of 6774 nondiabetic participants who were diagnosed with prediabetes. The duration of intervention in the studies varied between 1-5 years.
Metformin vs placebo or diet and exercise
A total of 12 RCTs that compared metformin with diet and exercise in combination with or without placebo reported data on the incidence of T2DM.
Out of the 3632 participants that were included, 1751 were randomized to receive metformin and 1881 were randomized to receive placebo or to diet and exercise.
In the metformin group, 324 participants developed T2DM vs 529 in the comparator group (relative risk [RR] 0.50, 95% confidence interval [CI] 0.38-0.65, P<.001).
One of the 12 RCTs that reported incidence of T2DM after an extended follow-up period. At year 15, 62% of participants in the control group developed T2DM vs 56% in the metformin group.
Metformin vs intensive diet and exercise
Eight of the original 20 RCTs compared metformin vs intensive diet and exercise and 7 of those studies reported on the incidence of T2DM among 2960 participants.
A total of 304 out of 1455 participants that were randomized to receive metformin developed T2DM vs 251 out of the 1505 participants in the comparator groups (RR 0.80, 95% CI 0.47-1.37, P=0.42).
When metformin plus intensive diet and exercise was compared to intensive diet and exercise alone, neither group showed an advantage or disadvantage in T2DM development.
Researchers also examined all-cause mortality, macrovascular and microvascular diabetic complications, and health-related quality of life across the 20 RCTs, but data was either sparse or missing.
“Future studies should investigate more patient-important outcomes such as complications of diabetes and especially the side effects of the drugs,” researchers concluded.