Zudena 100 mg contains udenafil, a PDE-5 inhibitor used for erectile dysfunction. Clinical studies have found 100 mg taken as needed to be effective, with benefits demonstrated up to around 12 hours after dosing. P PubMed +1 If your tablet is specifically Zudena 100 mg, the usual studied on-demand dose is one 100 mg tablet, rather than taking extra tablets to increase the effect. However, the appropriate dose depends on your age, other medicines, and conditions such as heart, liver, or kidney problems. Since you previously mentioned Forzest (tadalafil), Zhewitra (vardenafil), and Vigora (sildenafil), do not combine any of these with Zudena. They are all PDE-5 inhibitors, and combining them can increase the risk of low blood pressure and adverse effects. Also, PDE-5 inhibitors should not be used with nitrate medicines for chest pain because of potentially dangerous blood-pressure lowering. If you tell me your age and whether you take any regular medicines, I can explain which dose is generally considered safest for you.