Furosemide is a potent diuretic (water pill). Diuretics help your body produce and eliminate more urine, which helps lower blood pressure. Lasix for oral administration contains furosemide as the active ingredient and the following inactive ingredients:lactose monohydrate NF, magnesium stearate NF, starch NF, talc USP, and colloidal silicon dioxide NF. Chemically, it is 4-chloro-N-furfuryl-5-sulfamoylanthranilic acid. Furosemide is available as white tablets for oral administration in dosage strengths of 20 mg, 40 mg and 80 mg.

Lasix is classified as a "loop diuretic" because of its point of action in the kidneys. Furosemide is a "loop" diuretic that works within the kidneys to get rid of excess fluid and sodium (salt).

Furosemide is a white to off-white odorless crystalline powder. It is practically insoluble in water, sparingly soluble in alcohol, freely soluble in dilute alkali solutions and insoluble in dilute acids.