Sildenafil acts as the active ingredient in Cenforce pills. Sildenafil acts as the active ingredient in these pills. This drug is taken sometime before sex. After taking it, its effect remains for 6-7 hours. Cenforce should be kept away from small children and pets. Cenforce is also available in different strengths. A doctor must be consulted before taking Cenforce. Cenforce is the best tablets for sex problem. People below 18 years of age should not use this drug.