You may be the victim of a drive-thru caffeine blast right in the adenosine receptors! That’s a scientific way to say that if you need to get sharp and stay sharp for that client presentation, a couple of cups may be okay…or not.

Yes, it’s true. If you’re one of the genetically predisposed, highly caffeinated drinks such as coffee will actually make you feel worse, a lot worse.

Shall we meet in the breakroom to do a line of dark roast?

Think of coffee as a psychoactive drug, because it most definitely is. In fact, caffeine is an important component of many prescription medications, and you can buy it in its pure form in the pharmacy aisles. Like all drugs, it works great for many people but can cause real trouble for others.

If you have any trouble with anxiety, nervousness, the jitters or have full-blown panic attacks, so go easy on the Venti cups. If you speed past your limit, that presentation or sales call could end in shaking hands, the flop sweats and eyes nervously darting to find the nearest exit. That’s a big price to pay for that third cup, or, at least, your boss will think so.

Why me?

How does it happen that caffeine, on one hand, can make someone feel more alert and better able to focus, even increase athletic performance and yet, for a susceptible person, cause such a lot of trouble? Caffeine has a definite plan of attack.

Put not very simply, caffeine interferes with the brain’s ability to regulate reactions to stress and anxiety by binding to the A1 and A2a adenosine receptors. Every person has a different response to this onslaught, so it’s important to monitor how caffeine affects you personally. There are genetic studies available to determine definitively if you have this hypersensitivity, but why bother?

If you have trouble with shakiness, getting to sleep or calming down after munching some chocolate-covered coffee beans, then you should beware. If you have panic or anxiety disorder, keep caffeine to less than 200 mg a day. In a 2003 study by the University of Chicago and the University of Munster, Germany, it only took 150 mg of caffeine, about 8 oz. of coffee, to affect genetically susceptible people.

Think a power nap will help? Not at all. In fact, in another study at the University of California, San Diego, exercise was the only method that measurably reversed the effects of caffeine. Interestingly, exercise also helped the underlying disorders, so if you have anxiety, go for a run on the treadmill in the office gym instead of dosing at the espresso machine.

How much is too much?

Adults seem to get the benefit of caffeine between the amounts of 12.5 and 100 mg per day. The downside of fatigue, jitteriness, anxiety and headaches appear when 4 to 12 mg of caffeine per kilogram of body mass is ingested.

For a 175 lb. or 80 kg, man, safe limits would be from 320 mg to 960 mg. That ends up to be no more than five 8-ounce cups of brewed coffee or two Starbucks Venti regular brews at 416 mg each.

For a 135 lb. woman, converted to about 60 kg, the safety line lies between 240 mg and 750 mg. That would limit her to about three 8-ounce cups of brew, or two Starbucks Grande regular brews at 320 mg each.

To dose, or not to dose?

For most people, drinking caffeinated coffee, tea or sodas is harmless enough. Just keep it to less than 100 cups a day, at which point it’s fatal. Before depending on the positive effects of your shots of espresso, though, know your limits and how it affects you. Don’t waste those precious daily limits, though. Go for the good stuff!