Although Viagra, Viagra Soft, Cialis, Cialis Soft and Levitra are all treatments for erectile dysfunction, the dosages and the effects vary. The normal dosage for Viagra and Viagra Soft is 25mg, but the effects of Viagra only last for 4 hours. Whereas Viagra Soft effect can last for 6 hours or more. Cialis and Cialis Soft are taken in 20mg pills and their effects last for 24-36 hours. Levitra's effect last for 24 hours and is available in 20 mg pills. Viagra Soft and Cialis Soft should be put under the tongue until it dissolves. While Viagra, Cialis and Levitra should be taken with a glass of water.