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By Brian Alexander

New York Times columnist Maureen Dowd has discovered what many inexperienced users of marijuana discover: Eating weed can be a lot more intense than smoking it.

After eating a marijuana-laced candy bar during a trip to Colorado where cannabis is legal, Dowd made a rookie mistake. Having taken a bite of the bar, and felt, well, nothing much, she ate more, she writes in her Wednesday column in the New York Times. After an hour or so, she “felt a scary shudder go through my body and brain. I barely made it from the desk to the bed, where I lay curled up in a hallucinatory state for the next eight hours.”

Dowd later discovered she had consumed multiple doses. “Candy bars like that are supposed to be cut into 16 pieces for novices,” she writes. 

Dowd’s experience is a reminder that, like any drug — including alcohol and nicotine — marijuana’s active ingredient, THC, can alter the function of neurons in the brain.

As with many drugs, effects can depend on dose. Eating pot, whether in a cookie, brownie or candy bar, is different than smoking because the THC has to pass through the liver. That’s why effects are less predictable than smoking and can be delayed anywhere between half an hour to two hours. Higher doses, especially in people who don’t regularly use marijuana, can cause panic, paranoia or acute psychosis, especially in someone with a diagnosed psychiatric condition, research shows. Since effects are delayed when eating it the way Dowd did, inexperienced consumers can easily take too much.

Most importantly, THC affects the body’s endocannabinoid system, a system of chemicals in the brain (one key chemical is anandamide, based on the Sanskrit word for “bliss”) which are involved in memory, appetite and the sensation of pain. In the 1990s, scientists discovered two different cannabinoid receptors, CB1 and CB2. When an endocannabinoid chemical hits a receptor, it is instructing the cell to do something, like, say, eat. Experiments have shown that animals, including people, who have eaten a meal, and are satisfied, can become very hungry after consuming THC. The THC has activated parts of the brain regulating hunger.

Cannabinoids also affect mood and motivation, which is why Dowd’s bad trip is much like that of the 22-year-old medical student described by French scientists conducting a study published in 2005 in the journal BMC Psychiatry:

“One hour after the administration of 20 mg of dronabinol [a cannabinoid drug], he started to laugh a lot and after 90 minutes, he manifested a severe anxiety with symptoms of derealisation and depersonalization. He reported ‘watching himself lying on the bed’ and repeated several times the same questions at just a few minutes interval. Starting 2.5 hours after ingestion of dronabinol, and at the 4 hours and 5.5 hours post-ingestion series of tests, he was unable to perform the psychomotor tasks…”

A second test subject suffered paranoid delusions.

Extreme side effects are rare among most casual users, but scientists have known about marijuana’s possible psychotic effects for decades, especially with larger doses. And it can take a long time for the symptoms to go away because THC is fat soluble, meaning it stays locked away in our body’s fat cells and is released slowly, over time.

 Brian Alexander is a frequent contributor to NBC News and co-author of the book The Chemistry Between Us: Love, Sex, and the Science of Attraction