Health agency warns against marijuana use

Marijuana can be addictive, harmful and a gateway drug, according to research from the National Institutes of Health.

A new report in the New England Journal of Medicine by researchers from the National Institute on Drug Abuse (NIDA) at the NIH warns of the darker side of marijuana, as several states around the country have begun to legalize it.

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The study argues the drug is particularly harmful to teenagers whose brain development can be stunted from marijuana use.

“It is important to alert the public that using marijuana in the teen years brings health, social, and academic risk,” said Nora Volkow, lead author and NIDA director. “Physicians in particular can play a role in conveying to families that early marijuana use can interfere with crucial social and developmental milestones and can impair cognitive development.”

Volkow made similar statements in April before a House committee highlighting the split among federal agencies on drug policy; the Obama administration is taking a hands-off approach to state enforcement of marijuana laws.

Last week the House adopted a bipartisan amendment to prevent the Justice Department from interfering in states' implementation of their own medical marijuana laws.

Volkow and NIDA has been criticized by marijuana advocates in the past who say negative effects of the drug has been overblown and it is not addictive. However, the new study says there’s clear evidence long-term use leads to addiction.

“Approximately 9 percent of those who experiment with marijuana will become addicted,” says the report. “The number goes up to about 1 in 6 among those who start using marijuana as teenagers and to 25 to 50 percent among those who smoke marijuana daily.”

The research says mice who were exposed to marijuana early on were more susceptible to other drugs later in life because they felt less rewarded from weaker drugs, such as marijuana.

The report also warns marijuana potency has greatly increased. Tetrahydrocannabinol, or THC, the main active ingredient in marijuana, has gone up on average from 3 percent to 12 percent between the 1980s and 2012.

“Although these findings support the idea that marijuana is a gateway drug, other drugs, such as alcohol and nicotine, can also be categorized as gateway drugs, since they also prime the brain for a heightened response to other drugs,” said the report.

On the other hand, Volkow and her colleagues argue it might be that people who have addictive personalities might be more likely to begin with marijuana because it is more accessible.

The report notes legal drugs such as alcohol and tobacco have been more harmful than marijuana — not because they are necessarily more dangerous but because they are more available.

“As policy shifts toward legalization of marijuana, it is reasonable and probably prudent to hypothesize that its use will increase and that, by extension, so will the number of persons for whom there will be negative health consequences,” said the report.