Thanks to the higher dose, as-needed Cialis starts working quickly and typically reaches its peak concentration within two hours. Because patients with recent heart attacks or stroke, heart pains angina , heart failure, uncontrolled blood pressure or uncontrolled irregular heart beats, severe liver disease, and retinal eye problems were not studied with Cialis, Cialis is not recommended for these patients. People with heart conditions should never take ED medications without consulting a doctor. If you forget to take Cialis, take the missed dose as soon as you remember. Popular ED medications found online include: Viagra sildenafil : As the first FDA-approved PDE5 inhibitor for ED, sildenafil is taken 30 minutes to four hours before sexual intercourse to help achieve and maintain an erection. The generic versions are just as effective and much less expensive. In some cases, ED can cause a strain on relationships and impact self-esteem.Learn more about Cialis oral. 1. This is a generic drug. The average cost for 30 Tablet(s), 5mg each of the generic (tadalafil) is $ You can buy tadalafil at the discounted . Cialis lasts up to 36 hours in the body, while Viagra lasts 4–6 hours in the body. Both are taken 30 minutes before sex. Cialis can cause limb pain, while Viagra can cause vision change, rash. The most commonly reported side effects in patients treated with Cialis during the testing of the product were: headache. indigestion. back pain. muscle pain. flushing. stuffy nose. Patients who.