What is the effective duration of caffeine?

Caffeine has an effect on the body for 8 hours.

Many people have this false perception. Sodas have barely any caffeine. You're not suppose to feel any extra energy flow from drinking it. If you need an energy boost in the morning, try drinking coffee (just not Starbuck's cold frappucino that comes in small glass bottles) or energy drinks.

Actually, any hot drink helps to wake up. If you don't like coffee, drink tea. It might not have more caffeine than soda and won't keep you going for hours, but at least it will help you start your day.

Energy drinks like Red Bull, Monster and Rock Star last for about 3-4 hours. Hot black coffee lasts for about 2-3 hours.

Well usually I have a strong coffee every morning at around 7.30 am and I feel wide awake until around 1 pm :)