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Why coffee drinkers and stacker users sometimes get the shakes

Ever wondered why you sometimes get the shakes if you swallow slimming pills together with a dose of caffeine? Or even just from a couple of cups of coffee first thing in the morning? Probably because you haven't eaten anything first. This is the cautious conclusion that we draw from reading an article published over twenty years ago in the European Journal of Clinical Pharmacology.

The researchers wanted to know whether your hands start to shake after drinking beverages containing caffeine. Or more precisely: as a result of the caffeine in coffee, tea or soft drinks. Most of the stories about hand tremors from drinking coffee come from people who haven't eaten, so the researchers decided to investigate whether the tremor was the result of not eating, rather than from the caffeine.

The researchers got their subjects to eat first, normally, and then they gave them a 450 mg dose of caffeine. They measured the shakes by attaching a measuring instrument to the subjects' hands that recorded the tremors. The results are shown on the graph below left. Look at the broken line. The higher the curve, the more the test subjects shook and these were the ones that ate normally and took caffeine.

The researchers then repeated the experiment but did not give the subjects caffeine. Their shakes are represented by the solid line. The curves are almost the same. So if you have breakfast, your hands don't shake after drinking caffeine beverages.

Why coffee drinkers and stacker users sometimes get the shakes

Above right, the solid line shows hand shake after eating normally but not ingesting caffeine. The dotted line shows hand shake if you fast and don't take in caffeine either. Ergo: it's the fasting that makes your hands shake.

Now to the graph below left. The broken line: shakes while fasting with caffeine. The solid line: shakes if you fast without caffeine. No effect.

Why coffee drinkers and stacker users sometimes get the shakes

Above right, solid line: shakes after a normal breakfast with caffeine. Broken line: fasting with caffeine. Conclusion: fasting gives you tremors.

The research points to what caffeine users who experience morning shakes could do: eat breakfast.

The researchers are not sure of the mechanism involved in the effect, but they suspect that fasting increases the production of cAMP in the body's cells.

Eur J Clin Pharmacol. 1985;29(1):37-43.