People taking nitrates like nitroglycerin Nitrostat or isosorbide mononitrate Imdur should not take PDE5 inhibitors, as doing so could result in a dangerous drop in blood pressure. Before taking tadalafil, tell your doctor and pharmacist if you are allergic to tadalafil, any other medications, or any of the ingredients in tadalafil tablets. Counterfeit medicines can be very dangerous. However, some states require a live video consultation. Tadalafil is sometimes taken as needed, usually at least 30 minutes before sexual activity and not more often than once every 24 hours.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. headache. indigestion. back pain. muscle pain. flushing. stuffy nose. Patients who get back pain and muscle aches usually get them 12 to 24 hours after taking Cialis and these usually go away by. AdSave on 50, Brand Name & Generic Drugs With SingleCare®. Get Your Free Rx Coupon Now! Over 50K Customers Save on Prescriptions Each Week Using Free SingleCare® Discount : Maintenance, Accute, Branded, Generic.