Have you ever wondered why, after your fifth cup of coffee of the day, you're still not feeling fully awake? Why you can drink 10 cups of black tea and you're still yawning? Well, there are a number of possible reasons why caffeine may not 'work' for you. Some are genetic, and some are learned. There are also plenty of things you can do if this is you and you're looking for other ways to get that energy boost in the morning or after lunch.
Curious? Check out this gallery to understand why caffeine might not work for you, and what you can do about it.