As Floridians consider whether to legalize medical marijuana, stories of potential benefits to patients abound. Chemicals found in pot clearly can alter important physiological mechanisms.
What's less clear is risk.
Pretty much any FDA-approved medicine carries measurable risk — witness scary disclaimers in pharmaceutical ads.
But marijuana comes in strains with widely different chemical contents. Users can puff it, or eat it. They can imbibe heavily or lightly. Controlled, scientific studies weighing benefits against risks don't exist.
Amid the uncertainty, one of the nation's top drug officials has enlivened the marijuana debate by declaring in a prestigious publication that pot can be harmful.
In a review published Wednesday in the New England Journal of Medicine, Nora Volkow, director of the National Institute on Drug Abuse, outlines marijuana's negatives, based on her reading of the medical literature.
Short-term use can impair memory and learning, create temporary psychosis if taken in high doses and cause more driving accidents, Volkow states. Long-term use — particularly among those who start young — can increase the chance of permanent brain changes, addictive behavior, mental illness and loss of IQ.
"The popular notion seems to be that marijuana is a harmless pleasure,'' Volkow writes. But as policy shifts toward medical marijuana and legal recreational use, "so will the number of persons for whom there will be negative health consequences.''
Critics of Florida's Amendment 2, which would write medical marijuana into the state Constitution, hailed the review as an important warning signal leading up to the Nov. 4 vote.
"The research showing the harms of marijuana use continues to pile up,'' said Calvina Fay, executive director of St. Petersburg's Save Our Society from Drugs. "Some of these harms are so dramatic that they cannot be ignored any longer.''
If voters read the Volkow report and study the amendment's full language, Fay said, they "will see that this proposed constitutional amendment is not in the best interest of the families and communities of this great state.''
United for Care, the amendment's sponsor, has never argued that marijuana is completely benign, said executive director Ben Pollara.
"We're just saying it is certainly not a horribly dangerous substance. We're just saying it should be available to really sick people as a tool in their regular medical treatment, if that is what their doctor recommends."
People do not die from too much pot, Pollara said. "Look at that versus Advil and Tylenol, which we take on a regular basis and kills 10,000 people a year,'' referring to studies on the risks of those and other non-steroidal anti-inflammatory drugs.
Some highlights of Volkow's review:
• One in nine long-term marijuana users will become addicted, with physical symptoms of withdrawal, though Volkow acknowledges that almost three times as many people are addicted to alcohol.
• Some research indicates pot can also alter the brain's pleasure/reward centers, making people more prone to addiction to other substances.
• Regular use of marijuana is associated with increased anxiety and depression, though Volkow acknowledges that no one has proven pot actually causes these problems.
• In one long-term study, IQ points appeared to decline among people who started using as young teens, compared with non-users.
Mason Tvert, spokesman for the Marijuana Policy Project, an advocacy group, criticized NIDA "for prioritizing politics over science."
The IQ study has been discredited, he said. As for addiction, he said, studies have indicated that pot withdrawal is no worse than getting off caffeine.
NIDA fails "to acknowledge any of the well-known research that refutes, and in some cases completely debunks, their conclusions,'' Tvert said.
Particularly troubling aspects of Volkow's review involved young people who start using pot early, and smoke heavily.
Still-developing brains are more vulnerable to long-term exposure. Several studies indicate that youngsters who smoke a lot have fewer connections between brain cells.
This is important, Volkow said, because regular pot smoking among 12th-graders has been "steadily increasing" in "recent years.''
NIDA did not respond to a Tampa Bay Times request for data supporting that statement.
Studies have not found that legalizing medical marijuana leads to increased teen use. Further, measuring teen use is complicated by the fact that researchers rely on teens to report their own pot-smoking honestly. And it's possible to show a variety of trends depending on which age groups and time periods are considered.
Even the chart shown in Volkow's report indicates that pot use among high school seniors has been essentially flat among 12th-graders for the last three years — inconsistent with the "steady rise'' she writes about.
Stephen Nohlgren can be reached at email@example.com.