Cialis reaches its maximum effectiveness two hours after you take it. Phosphodiesterase type 5 PDE5 inhibitors. Nitric oxide is a substance that causes blood vessels to relax. The as-needed dose is usually 10 mg but can range from 5—20 mg. Data shared with Viatris will be aggregated and de-identified; it will be combined with data related to other Savings Offer redemptions and will not identify you Viatris reserves the right to rescind, revoke, or amend this Savings Offer without notice No membership fees.Learn more about what VIAGRA® (sildenafil citrate), a prescription treatment for ED. This Savings Offer is limited to 50% savings off the amount of your co-pay or your out-of .  · a light-headed feeling, like you might pass out. Common sildenafil side effects may include: flushing (warmth, redness, or tingly feeling); headache, dizziness; heartburn, nausea, or upset stomach. abnormal vision (blurred vision, changes in color vision) runny or stuffy nose, nosebleeds; sleep problems (insomnia); or. The recommended dosage of Viagra for erectile dysfunction (ED) is 50 mg, taken as needed about 1 hour before sexual activity. You can take it 30 minutes to 4 hours before sexual activity. And you.