Tadarise 20 mg contains tadalafil, which can have an effect for up to about 36 hours. That does not mean you’ll have an erection continuously—it means you may be able to get an erection more easily when *****ly stimulated during that period. A few important points: It usually starts working in 30–60 minutes. You still need ***** stimulation. Don't take more than one tadalafil dose in 24 hours unless your doctor specifically tells you otherwise. Do not combine Tadarise with sildenafil products such as Fildena, Silagra, or Super P-Force. Never combine tadalafil with nitrate medicines (e.g., nitroglycerin) because blood pressure can fall dangerously low. An erection lasting more than 4 hours is an emergency and requires immediate medical attention. If you're asking because you're considering Tadarise 20 mg for tonight, I can also explain the safest timing and what to avoid with it.