Zenegra 100 mg is available in pharmacies (including online pharmacy services in India), though it is generally a prescription medicine. It contains Sildenafil 100 mg and is used for erectile dysfunction (ED). A few points: Zenegra 100 mg is a higher strength than Zenegra 50 mg. It is usually taken only when needed, commonly about 30–60 minutes before sexual activity. Do not take more than one dose in Zenegra 100 mg  unless your doctor specifically advises it. A higher dose is not always better; many men respond well to 50 mg and may have fewer side effects. Possible side effects at 100 mg may include: Headache Flushing Dizziness Indigestion Vision changes Do not use it with nitrate heart medicines (such as nitroglycerin) because the combination can cause a dangerous drop in blood pressure. If you tell me your age and whether 50 mg sildenafil works for you or not, I can help explain whether 100 mg is usually considered appropriate.