Viagra 150 mg belongs to the phosphodiesterase type-5 (PDE 5) inhibitors drug class. It is primarily used to treat erectile dysfunction (ED). Sildenafil Citrate is its active component. You can buy Viagra online only with a doctor’s prescription. It can be used alone or with other medication. Viagra 150 mg is the best and well-recommended drug. Also used to treat pulmonary arterial hypertension (PAH) and improve exercise capacity in men.