Take tadalafil exactly as directed. You may attempt sexual activity at any time between doses. What special dietary instructions should I follow? Obesity Additionally, certain risk factors increase the risk of ED, such as smoking , lack of exercise, and drug or alcohol use. One of these is PAH. If you are taking tadalafil for erectile dysfunction on a regular schedule, take the missed dose as soon as you remember it.AdEnjoy Greater Libido & Performance. Fast Express Shipping. 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. Tadalafil (Cialis) is used to treat erectile dysfunction (ED, impotence; inability to get or keep an erection), and the symptoms of benign prostatic hyperplasia (BPH; an enlarged prostate) which include difficulty urinating (hesitation, dribbling, weak stream, and incomplete bladder emptying), painful urination, and urinary frequency and urgency in adult men.