Both Kamagra and Viagra contain the same active ingredient, sildenafil, and have similar effects and duration of action. Both medications usually start working within 30 to 60 minutes after taking them, though it may take slightly longer for some people. After taking the medication, the effects will usually last for 4 to 6 hours. However, you will only be able to get an erection when sexually aroused — the medication doesn't cause an erection on its own. Both Kamagra vs Viagra are not intended for daily use. They are typically taken as needed, about 30 minutes to 1 hour before sexual activity.