Erectile dysfunction drugs Cialis and Levitra work by relaxing muscles and increasing blood flow. While Levitra is taken about 1 hour before it is needed, Cialis can be consumed up to 12 hours before. Cialis effects can last up to 36 hours, earning it the moniker of the "weekend pill". Levitra and Staxyn are the same drug -- Vardenafil. Similarly, Cialis and Adcirca are the same drug -- Tadalafil. Adcirca is prescribed for treating pulmonary arterial hypertension.
Cialis is used to treat erectile dysfunction and the signs and symptoms of benign prostatic hyperplasia. Under the brand name Adcirca, it is also used to treat pulmonary arterial hypertension.
Levitra is also used to treat erectile dysfunction.
Cialis can be taken with or without food as needed, immediately before sexual activity. The 10mg tablets should be swallowed whole and not more than once per day. Cialis is also available in 2.5mg tablets that are taken every day.
Levitra can be taken with or without food. It is taken as needed in 10mg tablets about 60 minutes before sexual activity. It should not be taken more than once every 24 hours. Sexual stimulation is requirement for response to treatment.
edit Side effects
Common side effects of Cialis include warmth or redness in face, neck or chest, cold symptoms such as stuffy nose, sneezing or sore throat, headache, memory problems, diarrhea, upset stomach, muscle pain and back pain.
Common side effects of Levitra include warmth or redness in face, neck or chest, runny or stuffy nose, headache, dizziness, upset stomach and back pain.
edit Overdose symptoms
Cialis overdose symptoms include chest pain, nausea, irregular heartbeat and feeling light-headed or fainting.
Overdose on Levitra may lead to back pain, muscle pain or vision problems.
Cialis and Levitra should not be combined with any nitrate drug for chest pain or heart problems. You should tell your doctor before talking these drugs if you have heart disease, high or low blood pressure, seizures, liver or kidney disease, a blood cell or bleeding disorder, a stomach ulcer, hearing or vision problems, an eye disorder or physical deformity of the penis.
Initial studies on Levitra suggested that it was effective between 74% and 87% of the time. It is less effective for men with hypertension, dyslipidaemia or diabetes. 
Cialis is the only erectile dysfunction drug that can be prescribed as a once-daily pill. It is also effective for longer – up to 36 hours. It is also used to treat pulmonary arterial hypertension. It is preferable for people with tachycardia as it does not affect the heart in the same way as Levitra.
Levitra may also be prescribed to treat premature ejaculation.