Smoke a lot of weed as a teenager, and when you reach adulthood you’ll be more likely to have trouble falling or staying asleep, according to a new University of Colorado-Boulder study of more than 1,800 twins.

The study, published in the journal Sleep, comes at a time when cannabis is increasingly being marketed as a sleep aid in states where marijuana is legal, a press release stated.

The researchers said it adds to a growing body of evidence suggesting that while it may help some users fall asleep occasionally, chronic use can have negative long-term consequences, particularly for the young.

“People tend to think that cannabis helps with sleep, but if you look closely at the studies, continued or excessive use is also associated with a lot of sleep deficits,” said lead author Evan Winiger, a graduate student in the Institute for Behavioral Genetics. “Our study adds to that literature, showing for the first time that early use is associated with increased rates of insomnia later on.”

For the study, Winiger analyzed data from 1,882 young adults from the Colorado Twin Registry, which has been following twins for research since 1968. Each had completed surveys about their sleep habits, marijuana use and mental health.

They found about one-third of subjects who started using marijuana regularly before age 18 had insomnia in adulthood, compared to less than 20 percent among those who didn’t use cannabis regularly as teens.

The same pattern held true for a particularly hazardous form of insomnia known as “short sleep” (sleeping fewer than six hours per night on a regular basis). About one in 10 subjects who used cannabis regularly as teens grew up to be short-sleepers, while only about 5 percent of nonusers did.

People who started using marijuana after they turned 18 also had slightly higher rates of insomnia in young adulthood. These patterns persisted when controlling for depression, anxiety and shift work (which can all also impair sleep).

Lasting impact

Exactly why early cannabis use correlates with later sleep problems remains unclear, but several theories are emerging.

As Winiger explains, the human body has its own endocannabinoid system, producing chemicals much like the cannabinoids (CBD and THC) present in marijuana that bind to cannabinoid receptors in our brains and have been shown to influence cognition, emotions and circadian rhythm – or body clock.

“One theory is that these receptors are being desensitized or disturbed from all the cannabis use at a time that the brain is still developing, and that leads to waking issues later,” he said.

It could also be that cannabis use in adolescence leads to structural changes in the brain. Previous brain imaging studies have shown it can alter the developing prefrontal cortex. Or chronic use may set teens up for poor sleep habits, which linger into adulthood.

Genes may also be at play.

By looking at 472 identical twin pairs (who share 100 percent of their genetic makeup) and 304 fraternal pairs (who share only 50 percent), the researchers were able to infer to what degree the traits were inherited. They concluded that many of the same genes that contribute to the risk of early cannabis use are also associated with insomnia and insomnia with short sleep.

“It is possible that sleep problems could influence cannabis use, cannabis use could influence sleep problems, or common genetics could be responsible,” the authors wrote.

The study does not necessarily mean all strains of marijuana are bad for sleep in all people all the time, Winiger noted. Some previous studies show cannabis can help people fall asleep if used occasionally, but chronic use and higher concentrations can disturb sleep quality.

For teens though, there are added risks, he said. It’s not recommended.

“The brain is still changing until you are in your mid-20s. What you do when you are young can have a big impact.”

Other authors include professor Kenneth Wright, director of the Sleep and Chronobiology Lab; professor John Hewitt, director of the Institute for Behavioral Genetics; graduate students Spencer Huggett and Alexander Hatoum; assistant professor of psychology Naomi Friedman; and Christopher Drake of the Henry Ford Hospital Sleep Disorders and Research Center.

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