Yes, ED pills can cause side effects. In addition, consider the information below. Nitrate-containing medications: Viagra Sildenafil should never be taken with any medications that contain nitrates. All PDE5 inhibitors, including Viagra and Cialis, require a valid prescription regardless of the pharmacy or provider. Cialis vs. In addition, ED is extremely common.Dosage. The dose of Cialis you need will depend on whether you’re taking it daily or as needed. Daily doses are often between and 5 milligrams (mg). The as-needed dose is usually 10 mg but can range from 5–20 mg. The typicaldose of Viagra is 50 mg. However, the dosage can range from 25– mg. Viagra (sildenafil) as low as. $ View other PDE5 Inhibitors. Sildenafil (Viagra, Revatio) is a moderately priced drug used to treat erection problems in men. It is also used to treat pulmonary arterial hypertension, a serious heart and lung condition. This drug is more popular than comparable drugs. It is available in generic and brand versions. Viagra (Sildenafil) belongs to a group of medications called phosphodiesterase type 5 inhibitors. It is used for the treatment of Erectile Dysfunction (male impotence). It helps to achieve and keep an erection sufficient for sexual activity. It does this by allowing a greater blood flow into the penis when a man is sexually aroused.