What special dietary instructions should I follow? This increased blood flow can cause an erection. Talk to your doctor about which dosing schedule is right for you. Side Effects Along with its needed effects, a medicine may cause some unwanted effects. By doing so—combined with sexual stimulation—a cascade of events occurs that increases nitric oxide.Both Cialis and tadalafil treat ED at the following doses: mg. 5 mg. 10 mg. 20 mg. At 20 mg, both drugs are also approved to treat symptoms of benign prostatic hyperplasia (BPH), such as difficulty urinating. They work by relaxing the muscle cells in the prostate, allowing urine to flow out of the bladder. Whichever condition Cialis is used to treat, the recommended maximum dose per day is 20 mg. This is the highest dosage that a doctor may prescribe. Dosage for erectile dysfunction (ED). The drug comes in low-dose versions that can be taken daily. This means you can have sex at any time, rather than needing to take a pill from time to time as needed like other ED brands. The starting dose for daily-use Cialis is milligrams (mg). If that doesn’t work, you can increase your daily dose up to 5 mg.