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In these early days of the holiday season, as cooks begin sifting through recipes rich in spice and sugar, consider this small warning from toxicologists: Measure your nutmeg carefully.

Very carefully.

Of all the well-loved seasonal spices, nutmeg stands out for its long and slightly twisted history. In the Middle Ages, it was used to end unwanted pregnancies. More recently, desperate prisoners embraced it as a rather miserable drug substitute. So, on occasion, have teenagers, some of whom wound up at poison control centers. A couple of years ago, a man in Sweden claimed that nutmeg had induced him to spit at strangers on the street.

“It’s not that nutmeg cases are that common,” said Leon Gussow, an Illinois toxicologist who publishes a blog for professionals called The Poison Review. “But toxicologists do recognize it as one of the more interesting spices in the kitchen.”

As Dr. Gussow noted recently in Emergency Medicine News, awareness of the spice’s poisonous and exotic side effects has been around for some time. Nutmeg is the seed of an evergreen tree, Myristica fragrans, native to Indonesia although now cultivated widely. The spice mace comes from a thin protective layer that encloses that seed.

The spice trade first brought nutmeg to Europe in the 12th century, where it rapidly gained a reputation as a seed of unusual potency, strong enough to fight infection (including the Black Plague), stimulating enough to bring on menstruation, poisonous enough to induce an abortion. It also earned shady credentials for inducing a kind of hazy, druglike high that could include hallucinations.

The effect was potent enough that nutmeg mythology eventually became part of prison culture, even into modern times. In the 1965 book, “The Autobiography of Malcolm X,” the activist describes purchasing it from inmates in prison, concealed in matchboxes, and stirring it into water. “A penny matchbox full of nutmeg had the kick of three or four reefers,” he wrote.

Toxicologists say that description is somewhat misleading, an overly romantic account of nutmeg’s generally unpleasant effects. It takes a fair amount of nutmeg — two tablespoons or more — before people start exhibiting symptoms. These can include an out-of-body sensation, but the most common are intense nausea, dizziness, extreme dry mouth, and a lingering slowdown of normal brain function. Dr. Gussow said nutmeg experimenters have compared it to a two-day hangover.

“People have told me that it feels like you are encased in mud,” said Dr. Edward Boyer, professor of emergency medicine and chief of the division of medical toxicology at the University of Massachusetts Medical School. “You’re not exactly comatose, but you feel really sluggish. And your remembrance of events during this time period is incomplete at best.”

The main chemical culprit in nutmeg is called myristicin which forms naturally in the seeds (and in other plants, occurring in trace amounts in carrots). Myristicin belongs to a family of compounds with psychoactive potential that occasionally are used to make much stronger psychotropic drugs. It has been included in recipes for MMDA. And it is chemically related to another compound, safrole, also found in nutmeg, which is sometimes used in the synthesis of the street drug Ecstasy.

Of course, this doesn’t mean that the natural compound acts like these synthetic drugs. “But a junior chemist might think that you are going to end up with a similar effect,” Dr. Boyer said. And he suspects that is one reason many of the poisoning cases seen in the United States involve teenage home experiments.

Still, nutmeg incidents are rare — at least, those reported to the authorities. “We do see a few pediatric cases where parents left an open spice jar where a child could reach it,” said Dr. Patrick Lank, an assistant professor of emergency medicine at the Feinberg School of Medicine at Northwestern University.

Dr. Lank was a co-author of a recent paper tracking 10 years of nutmeg poisoning, as reported to Illinois poison control centers.

The authors discovered 32 cases in a 10-year period; 17 were accidental and 15 were deliberate. Of the deliberate cases, most involved young people between the ages of 15 and 20 who were mixing nutmeg with pharmaceuticals. Of that group, one had such a bad reaction that he ended up on a ventilator.

“Adolescents can have really bad effects when they mix nutmeg with other things,” Dr. Lank warned. A study in California, tracking 119 incidents involving nutmeg from 1997 to 2008, reached a similar conclusion, although the authors found a higher level of deliberate abuse. In that case, 72.3 percent of the poisoning cases involved intentional use.

“Abusers were significantly more likely to require medical evaluation than non-abusers,” the authors noted. But, as with the Illinois study, they reported no fatalities.

Dr. Boyer said he has seen just two cases of nutmeg poisoning that required hospitalization in 15 years, and both of those were teenagers looking for a high. “They recovered more slowly than we expected, and then the nutmeg story crept out,” he said.

The rarity of the cases means that even though nutmeg information is available online, there is enough information about the negative effects that most people appear to avoid it anyway. “It’s clear that the stories on the Internet have not led to large numbers of nutmeg abusers turning up in emergency rooms,” Dr. Boyer noted.

The usual holiday samplings of nutmeg — the dusting on eggnog or a cocktail, the quarter-teaspoon sprinkle that goes into a pie or cake — is not a risk to revelers. In those doses, the woodsy, sweet flavor should simply be enjoyed.