The LD50 (the dose that is lethal to 50 percent of the population) for caffeine in humans is estimated to be 5000 mg. But in the presence of certain drugs that block caffeine metabolism, this amount can decrease by up to five-fold. There are about 80 drugs, including antibiotics, antidepressants and decongestants) that can do this. So, in a worst-case scenario, 1000 mg of caffeine (equivalent to 10 No Doz pills) can be very harmful--even fatal. Yet, a 24 ounce can of Monster Energy Drink supposedly (we'll get to this later) contains between 240 and 550 mg of caffeine. Assuming the higher amount, it is not difficult to see why a 14-year old girl weighing 90 pounds and taking Cipro could end up in the emergency room (or worse) by drinking two cans of the stuff.

Now for the idiocy. How much caffeine is actually in two cans of Monster Energy Drink? No one really knows. This is because these drinks are considered to be supplements and are therefore exempt from FDA labeling requirements.

Jacob Sullum puts things in perspective: