Diuretics remove fluid from the body by making people urinate more. This can cause dehydration if too high a dose is taken. Adverse effects on kidney fuction, serum sodium and serum calcium levels may be seen. They can affect sexual potency in men. However, these medications are safe and well tolerated by the vast majority of patients taking them.
Any side effect resolves with discontinuation of the medication.
Spironolactone is a diuretic that also inhibits the effects of a hormone called aldosterone. This hormones is deleterious to failing hearts. Spironolactone has been shown to improve symptoms and survival in patients with severe heart failure due to weakened heart muscle independent of and in addition to its fluid removing effects.