• Viagra originally developed to treat angina sufferers was later discovered to help the cause of erectile dysfunction. Levitra is relatively a new revolutionary drug used to treat Erectile Dysfunction also.
  
  
• Viagra works in about 30 minutes and lasts for at least 4 hours. Peak levels of erection were reached in mean times of 30 minutes and 36 minutes after taking Levitra. Levitra stayed active and working in the system for an average of 12 hours in patients 65 years or older, and 9 and a half hours in younger participants. Clinical studies have shown that Viagra has the ability to remain in the system for up to 4 hours.
  
  
• When a man is sexually aroused, certain tissues in his penis relax. This allows large amounts of blood to flow in, thus producing an erection. Viagra helps by elevating the levels of the chemical that causes the tissues to relax. Levitra acts in the same way as Viagra, by blocking an enzyme called phosphodiesterase-5, or PDE-5. This helps the smooth muscles in the penis to relax, which effectively increases blood flow.
  
  

  DRUGS	CIALIS	LEVITRA	UPRIMA	VIAGRA
  Manufacturer	Lilly Icos	Bayer	Abbott Laboratories	Pfizer
  Date Introduced	Feb 2003	April 2003	June 2001	March 1998
  Dosage	5mg,10mg,20mg	5mg, 10mg,20mg	2mg,3mg	50mg,100mg
  Average Approx. Absorbtion Rate	20 Minutes	40 Minutes	20 Minutes	40 Minutes
  Duration Of Effectiveness	36 Hours	4 Hours	4 Hours	4 Hours
  Reported Side Effects	Headache, Myalgia, Dyspepsia, Back Pain	Headache, Flushing, Dyspepsia, Nasal Congestion	Headache, Nausea, Dizziness	Congestion, Diarrhea, Flushing, Headaches, Urinary Tract Infection, Bluish Vision
  Contraindications	Any Nitrate-Based Medicine, Angina, Hypertension, Hypotension	Any Nitrate-Based Medicine	Angina, Myocardial Infarction, Anti-Hypertensive Nitrates	Any Nitrate-Based Medicine

  
  
• Viagra achieved a success rate of 60-80 per cent, depending on the dosage, in trials. However, it doesn't always work first time as claimed by some. Levitra, by comparison, works for 72-90 per cent of men the first time and goes on to work 95 per cent of the time.
  
  
• Blue discoloration of vision (overlap with PDE-6 in the retina) is seen only with Viagra (<0.5%), whereas headache, facial flushing, and mild indigestion were observed with Levitra. Viagra can cause some visual problems, including, an increased sensitivity to light, blurred vision, or an inability to tell the difference between blue and green.
  
  
• VIAGRA is available in the strength and pack of 50mg, 100mg (4-8 comp.) / 100mg (30 tablets USA) whereas Levitra is available in 5mg, 10mg and 20 mg. 4 or 8 comp.