Drug Uses Viagra is used in the treatment of erectile dysfunction. Viagra helps the flow of blood into the male organ and maintains erection while performing sexual activities. Cialis helps men to achieve and sustain an erection for longer periods while having sexual activities. It is an oral medication. Benefits of Cialis: When compared to Viagra and Levitra, Cialis’ effects last longer (upto 48 hours). Cialis also has fewer side effects. Cialis is meant for daily use so that you can be prepared anytime. Levitra helps men to have stronger erections during sexual activities. It dilates the blood vessels of the penis thereby helping more blood to flow into it. This leads to a stronger erection. Usage Viagra is generally taken 30 minutes to 1 hour before sexual activity. Viagra can also be taken 4 hours before sexual activity. The dosage should not increase more than once in a day (24 hours). You must always follow your doctor’s dosage instructions while taking Cialis. If you still have any doubts then there will be detailed dosage instructions on the medicine label. Cialis comes in various doses like 5mg, 10mg and 20 mg. The ideal dose for starting with Cialis is 10mg once a day. You need to take it half an hour before sexual activity. You may choose to take Levitra with a meal or without one. The drug works best when taken 30 to 60 minutes before initiating sexual activity. The dosage should not increase more than once in a day (24 hours). Drug Class and Mechanism Viagra helps to treat impotence in men. It is a phosphodiesterase type 5 inhibitor. Viagra helps increase the blood flow into the penis thereby maintaining an erection during sexual activities. Cialis is a phosphodiesterase inhibitor type 5. It works by helping the blood flow into a penis to achieve and maintain an erection. Levitra is a phosphodiesterase inhibitor that works by helping blood flow into a penis to achieve and maintain an erection. Missed Dose Since Viagra is an erectile dysfunction drug, it must only be used when required. So, there are no chances of a missed dose since it is not taken according to a regular dosage schedule. You need to take Cialis only before any sexual activity. You cannot take Cialis more than one dose a day. Since Levitra is an erectile dysfunction drug, it must only be used when required. So, there are no chances of a missed dose since it is not taken according to a regular dosage schedule. Never take two doses at one time. Storage Store Viagra at room temperature between 59 and 86 degrees F (15-30 degrees C). Protect it from direct exposure to light, heat and moisture. Keep away from children and pets. Store Cialis at room temperature. Store Levitra at room temperature.