If you are taking tadalafil for erectile dysfunction on a regular schedule, take the missed dose as soon as you remember it. Sexual activity may be a strain on your heart, especially if you have heart disease. Tadalafil is its active ingredient and is available as a generic drug. Your doctor will probably tell you not to take tadalafil if you are taking street drugs containing nitrates. Do not take more or less of it or take it more often than prescribed by your doctor. Do not take a double dose or more than one dose per day to make up for a missed one.Cialis doesn’t work right away. For the as-needed dose, plan to take Cialis at least 30 minutes before sexual activity, but bear in mind it may take as long as 2 hours to take effect. Tadalafil (Cialis) is taken by mouth either as needed before sexual activity or once daily for erectile dysfunction (ED).It’s also taken once daily to treat symptoms from an enlarged prostate (benign prostatic hyperplasia, or BPH).Tadalafil (Cialis) is available both as brand-name and generic tablets. Common side effects of this medication include .  · But on average, its effects start to lessen 2 to 3 hours after you take a dose. The typical dose for once-daily Cialis for ED is milligrams (mg) to 5 mg. When used as needed for ED, the usual.