Who should not take Cialis? Will Cialis be prescription or OTC over-the-counter? What special dietary instructions should I follow? If you are taking tadalafil on a regular schedule, take it at around the same time every day. If you become pregnant while taking tadalafil, call your doctor. Cialis is not recommended for people taking any form of nitroglycerin because the combination may lower blood pressure to an unsafe level.Oral medications, like Viagra and Cialis, which require a prescription and are commonly used to treat ED, can take 30 minutes to take effect, she adds. Injections take less time to work, but they. Get the facts on five over-the-counter ED pills. Learn how options like DHEA and yohimbe can help treat erectile dysfunction. Learn about warnings and more. MNT ‘s review At Hims, Cialis is available as: Daily tadalafil: or 5 mg daily pill Tadalafil: 5 mg, 10 mg, or 20 mg, taken as needed Cialis: mg, 5 mg, 10 mg, and 20 mg, taken as needed.