You may also be able to get your prescription through an online healthcare provider, like Felix. If you already have a prescription, you can also have it transferred to Felix so that you can start ordering Cialis online rather than having to go to the pharmacy every time you need it. Do not take more or less of it or take it more often than prescribed by your doctor. What alternatives can I use for erectile dysfunction? Your doctor will discuss the best treatment plan for you.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. AdComplete the Online Consultation with our Doctor. Personalize Your Needs. If Appropriate, Get a Prescription for ED from RexMD®. Free Shipping AvailableReal Doctors · Free Shipping · Personalized Plan · Discreet Packaging. Cialis is approved by the FDA to treat erectile dysfunction (ED). Our medical team can prescribe Cialis 5mg, 10mg, and 20mg. The starting dose we generally recommend is 10mg. Tadalafil is the name for the active chemical ingredient in Cialis.