Zenegra 100 mg contains sildenafil 100 mg, a PDE5 inhibitor used to treat erectile dysfunction (ED). It works by increasing blood flow to the penis during sexual stimulation, helping men achieve and maintain an erection. 

Zenegra 100 mg can be effective, particularly when lower sildenafil doses have not provided adequate results. However, 100 mg is the maximum recommended sildenafil dose for ED, and it is not necessarily more appropriate or effective for every man. The usual starting dose is 50 mg, which can be adjusted to 25 mg or 100 mg depending on effectiveness and tolerability. It should not be taken more than once in 24 hours. 

Sildenafil generally works when taken about one hour before sexual activity, although it can be taken approximately 30 minutes to 4 hours beforehand. Sexual stimulation remains necessary, and a heavy meal may delay its effect. 

Common side effects include headache, flushing, indigestion, nasal congestion, dizziness, and visual changes. Zenegra should not be used with nitrate medicines such as nitroglycerin because the combination can cause a dangerous drop in blood pressure. 

Zenegra 100 mg can effectively treat ED, but the appropriate dose depends on individual response, health conditions, and other medicines. It should be used under medical guidance.