But, keep in mind that ED might signal an underlying medical problem, like high blood pressure, heart disease, diabetes, low testosterone, or sleep apnea. Some examples of nitrates are nitroglycerin Nitro-Dur, Nitrostat, others , isosorbide mononitrate Monoket and isosorbide dinitrate Bidil. They enhance the effects of a chemical the body makes that relaxes muscles in the penis, called nitric oxide. Your healthcare provider can help you determine the right dosage for you. 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. It works for up to 36 hours. Oral ED medications are generally well-tolerated, Dr.Cialis is a long-lasting erectile dysfunction treatment, and is effective for up to hours. Cialis is available as tablets that you take daily (mg or 5mg) or just before you want to have sex (10mg or 20mg). The active ingredient in Cialis is Tadalafil, which is available as a generic medication. You can order Cialis from Superdrug Online. Get Cialis and Tadalafil pill online. Try the generic Cialis option for a fraction of the cost, after speaking with one of our online medical professionals. Cialis comes in several different strengths, including: milligrams (mg) 5 mg. 10 mg. 20 mg. The cost for these different strengths depends on whether you have insurance, your individual plan.