4/06/2004 12:58:00 PM

Jittery? Peevish? Can't Sleep? What Are You Drinking?

In general, more than 1.5 grams of caffeine a day can cause the typical symptoms of caffeinism: anxiety, insomnia, irritability and palpitations.

Caffeine is far and away the most widely used stimulant in the world. It is actually a member of a class of compounds called xanthines that includes theobromine, which is abundant in chocolate and theophylline, the major xanthine in tea.

Caffeine works by blocking the calming and analgesic effects of the neurotransmitter adenosine in the brain. In moderate doses, caffeine enhances arousal and performance. At higher doses, caffeine blocks a majority of adenosine receptors and can produce anxiety and hypersensitivity to pain.

...Judging from the sheer number of consumer products spiked with caffeine, one would think we were a nation of narcoleptics, desperately trying to stay awake.