BackgroundNigella sativa (black cumin) and Cinnamomum cassia (Cinnamon) are an integral part of the Indian diet, and have also been sourced in the ayurveda, the traditional Indian system of medicine, for their medicinal properties. Both the herbs individually have been successfully evaluated for their preliminary antidiabetic potential.ObjectiveHerein, we dived deeper into antidiabetic properties of these herbs, by investigating the combinatorial effect of both herbs, on parameters of diabetes and further, as an adjunct to metformin therapy, for assessing the pharmacodynamics of herb-drug interaction in diabetes mellitus. The objectives were to screen the combinatorial extract of Nigella sativa & Cinnamomum cassia’s (NSCCe) alone and in combination with metformin for its potential in mitigating symptoms of diabetes mellitus-alone, and as an adjunct therapy with metformin.Materials and methodsDiabetes was induced in the animals by a single intraperitoneal injection of streptozotocin. Animals were divided into seven groups with 6 animals each: Vehicle control, Negative control, Positive control (Metformin 50 mg/kg), treatment groups 4 and 5 received NSCCe at the doses of 100 mg/kg and 200 mg/kg, respectively. Groups 6 and 7 received the same doses, in combination with Metformin (50 and 25 mg/kg). Following a 28-day dosing period, plasma glucose levels, lipid profile and renal function profile were evaluated. Histopathological examinations were performed to measure any morphological change in kidney, liver and pancreatic tissue.ResultsCombination of Nigella sativa & Cinnamomum cassia extracts significantly normalized plasma glucose levels, lipid profile and kidney function parameters, compared to the diabetic control group. Animals treated with the combinatorial extract and metformin showed more prominent effects on these parameters. Significant reversal in the pancreatic cell damage was observed on treatment with NSCCe.ConclusionThis study generates evidence to support Nigella sativa & Cinnamomum cassia as an adjunctive in diabetes treatment protocols.