Are you overdoing your caffeine habit?

"People often don't understand the potential risk of these beverages," University of Florida's director of forensic toxicology, Bruce A. Goldberger, told Chemical and Engineering News. "Caffeine is a stimulant and, when consumed at high enough levels, can have negative effects."

"Whereas low-dose caffeine effects are wakefulness, a little bit of arousal, and slight euphoria," Bertil B. Fredholm, emeritus professor of pharmacology at Sweden's Karolinska Institute, said in the report, "high-dose effects are anxiety, irritation, and general mental discomfort -- a completely different kettle of fish."

Yet scientists say that tolerance levels for caffeine can vary widely between individuals. Drug use can also affect caffeine tolerance. Women who take contraceptive pills break down caffeine more slowly, while smokers tend to process the stimulant at a faster pace than non-smokers.

Grande (16 oz./ 473 mL) cup of Starbucks coffee: 330 mg 2 oz./59 mL show of 5-Hour Energy: 215 mg

8 oz./236 mL cup of coffee (brewed): 133 mg 20 oz./591 mL bottle of Pepsi Max: 115 mg 8 oz./236 mL cup of coffee (instant): 93 mg 8 oz./236 mL can of Monster Energy : 92 mg 20 oz./591 mL bottle of Mountain Dew: 90 mg 8 oz./236 mL can of Red Bull Enegy Drink: 83 mg 2 oz./59 mL cup of espresso: 80 mg