The drug-herb combination between metformin and bitter gourd needs further study of the benefits and risks. This study aims to explore metformin in plasma samples using the HPLC method and its pharmacokinetic profiles affected by the bitter gourd. This experimental method study with a post-test randomized controlled group design. Healthy albino rabbits were divided into three groups (n=3). They were administered with bitter gourd juice 100% (4 ml/kg BW) and metformin (BM1), bitter gourd juice 50% (4 ml/kg BW), and metformin (BM2), and metformin 26 mg/kg (M). BM1 and BM2 were given bitter gourd juice for 14 days, and then a single dose of metformin was given to all groups on the 15th day before metformin pharmacokinetic parameters were measured. Blood samples were collected from marginal ear vein punctures at 0, 10, 30, 60, 120, 240, 360, and 480 minutes. The plasma was analyzed using HPLC methods, and the concentration vs. time was used for a 1-compartmental open model pharmacokinetics analysis. Bitter gourd juice with 100% (4 ml/kg BW) concentration decreased the V/F and CL/F, also increased Ka, T1/2, Cmax, MRT, and AUC0-inf, also significantly increased AUC0-480, and decreased Tmax (p < 0.05). The pharmacokinetic interaction of metformin and Momordica charantia L. is presumably because of the competitive interaction between phytochemical constituents of bitter gourd and metformin on the OCT and MATE transporter.