Metformin has been the most widely prescribed medicine for type 2 diabetes for more than 60 years. Millions of people take it every day because it helps lower blood sugar, is affordable, and has a long record of safety. Their experiments showed that metformin lowers blood sugar by reducing the activity of Rap1 in this part of the brain. When these mice received low doses of metformin, the medicine no longer lowered their blood sugar. Even though the doses were thousands of times smaller than those taken by mouth, blood sugar levels still fell significantly.