Diabetes mellitus (DM) represents a global health problem characterized by hyperglycemia due to insufficient insulin secretion or failure of insulin activity. There is an imperative need for the discovery of alternative therapeutic agents that overcome the drawbacks of the current synthetic antidiabetic drugs.

This review critically summarizes the reports on the known and novel natural compounds, including alkaloids, flavonoids, and saponins with a potent antidiabetic activity that were recently published from 2014 to 2019. We discussed the underlying mechanisms of action that put these compounds in the category of effective antidiabetic candidates.

Information was obtained from Google Scholar, Scirus, PubMed, and Science Direct.

The reported natural compounds showed promising antidiabetic activity through different mechanisms such as the inhibition of α-amylase, α-glucosidase, insulin-sensitizing effect, direct action on protein tyrosine phosphatase 1B (PTP1B), peroxisome proliferator-activated receptors (PPARs), GLUT4 expression, insulin receptor substrate-1 (IRS-1) and glycogen synthase kinase-3β (GSK-3β) as well as dipeptidyl peptidase-4 (DPP-4) enzyme. Some compounds inhibited the formation of advanced glycation end products (AGEs). Other compounds prevented the risk of diabetic complications such as cardiovascular diseases, retinopathy, and nephropathy. This review provides a critical overview of the most recent discoveries of antidiabetic agents from natural sources. This overview could help researchers to focus on the most prominent candidates aiming to develop new drug leads.