The correct answer is option 1: Metformin. Metformin is an oral medication commonly used as an anti-diabetic drug to treat type 2 diabetes mellitus. It belongs to the class of medications called biguanides. Metformin helps lower blood sugar levels by improving insulin sensitivity, reducing the amount of glucose produced by the liver, and decreasing glucose absorption in the intestines. It is usually prescribed along with a healthy diet and regular exercise to manage diabetes.

Option 2, Zolpidem, is not an anti-diabetic drug. It is a sedative hypnotic medication used for the short-term treatment of insomnia.

Option 3, Promethazine, is an antihistamine medication used to treat allergic conditions, nausea, and vomiting.

Option 4, Hydralazine, is an antihypertensive medication used to treat high blood pressure.

Alert - correct answer should be option 1.