Its effects might last longer if you have mild to moderate ED. You can take Viagra daily, but because the medication stays in your system for four to six hours, it will not be effective all day. Cialis: Is one right for you? Can I trust online reviews about Cialis? However, because sexual stimulation is required to initiate the local penile release of nitric oxide, tadalafil’s inhibition of PDE5 will have no effect without sexual stimulation. Cialis can be taken daily, providing constant treatment for ED for people who have sex frequently.not available over-the-counter (OTC) Was this helpful? How does Cialis work? Cialis works by increasing blood flow to the penis to help a person get and maintain an erection. It also blocks. 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. Promotion disclosure info Save up to 97% on tadalafil cialis with GoodRx Different pharmacies offer different prices for the same medication. GoodRx helps find the best price for you. See all tadalafil cialis prices If you’ve ever looked into getting a medication for erectile dysfunction (ED), you may know that treatment prices can vary.