1-Hydrazinophthalazine Hydrochloride, commonly known as Hydralazine Hydrochloride, is a pharmaceutical compound primarily used as an antihypertensive medication. It functions as a direct-acting vasodilator that relaxes arterial smooth muscle, thereby reducing peripheral vascular resistance and lowering blood pressure. This makes it effective in treating hypertension and heart failure. In medicinal chemistry, it serves as a key building block and intermediate for synthesizing related pharmaceutical compounds targeting cardiovascular diseases. Additionally, research has explored its potential in cancer therapy, where it may inhibit DNA methyltransferases or other pathways involved in tumor growth, and in biochemical studies of enzyme mechanisms and novel therapeutics.