Although I went off chocolate when I became pregnant as part of a general zero-drug-tolerance policy, I've never considered chocolate's caffeine content to play a significant role in my life.

I have nibbled chocolate at various times of the day, and even late at night, without suffering the slightest bit of sleeplessness once I turned in.

But a friend of mine swears that if she has even a small quantity of chocolate after about three in the afternoon, she's up until all hours of the night. "It's just like drinking a cup of coffee," she insisted once.

That didn't sound right to me. I knew chocolate had some caffeine -- at least, I knew in an "everyone knows that" kind of way. But exactly how much did it have, and was it really enough to keep even a small woman like my friend up all night?

It was time to do some research. As often happens when one starts out with a seemingly simple question, the answer was more complicated than I had expected.

More than one web site I happened across insisted that chocolate has no caffeine at all. Instead, they said it contains a bitter alkaloid called theobromine, a cousin of caffeine and, like caffeine, a stimulant.

Perplexed, I looked further. Both popular and almost-too-scientific-for-me-to-understand sites agreed that chocolate does indeed contain theobromine -- a chemical whose name means "food of the gods." Which would be an appropriate title for chocolate itself.

Sadly, the presence of theobromine is what makes chocolate poisonous to pets, especially dogs. Several web sites have confirmed that cocoa products should be kept away from domestic animals.

Did the presence of the stimulant theobromine rule out caffeine in chocolate? Were references to "caffeine" in chocolate simply, as one site claimed, shorthand for the chemically-similar theobromine?

Was chocolate therefore safe for people allergic or otherwise sensitive to caffeine?

I did some more reading, and wrote a letter to Jaime Foster, Program Specialist in the department of human nutrition at Ohio State University.

In her reply, she stated that chocolate contains both theobromine and caffeine.

Caffeine occurs in smaller quantities, however. According to the U.S. Pharmacist web site, the two naturally-occurring chemicals make up about 3% of a cocoa bean, with theobromine outweighing caffeine by about two to one.

In spite of being so closely related, caffeine and theobromine have very different effects on human beings. Caffeine is a stronger stimulant and acts relatively quickly as a wake-up drug; theobromine tends to induce a mild sense of well-being over a longer period of time.

Though the caffeine in chocolate should certainly be taken into account, keep it in perspective. One ounce of milk chocolate has about the same amount of caffeine as an average cup of decaffeinated coffee. A little -- still enough to worry about if you're allergic or very sensitive.

The darker the chocolate, of course, the higher the caffeine content -- but you'd still have to eat an eight-ounce bar of semi-sweet to get anywhere near the caffeination of a cup of real coffee.

My friend who can't eat chocolate past three is a milk chocolate lover. Perhaps the sugar in the candy she's eating is what's keeping her awake?