OBJECTIVE. To investigate the effect of metformin on testosterone levels in men with type 2 diabetes mellitus (T2DM).RESEARCH DESIGN AND METHODS. Seventy m
diabetesjournals.org
RESULTS
Total, free, and bioavailable testosterone increased significantly within 5 days (all
P < 0.001). After 1 month, compared with the control group, the metformin group had lower total (12.7 vs. 15.3 nmol/L), free (0.20 vs. 0.24 nmol/L), and bioavailable (4.56 vs. 5.31 nmol/L) testosterone (all
P < 0.05).
So metformin did cause a significant reduction in endogenous testosterone production after 1 month. It is thought that metformin inhibits cytochrome P450-C17a, a key enzyme in the synthesis of steroid hormones. However, the longer-term effect of metformin on testosterone and sexual function remains uncertain. Obviously from your blood testing
@mcs, there was also a significant reduction in total T levels after about 6 months of use. But as you pointed out, being on TRT should keep the levels higher.
Observation - lots of competitive bodybuilders use metformin in the bulking cycle to avoid putting on body fat while consuming extra calories and carbohydrates. It also helps avoid insulin resistance with high doses of HGH. Metformin increases glucose uptake into muscle tissue (incresed sarcoplasmic hypertrophy) while simulating fat loss, improves cholesterol values, and results in an overall improvement in metabolic health.