The question of why some kids start using alcohol, cigarettes, marijuana, and other drugs at a young age remains a source of controversy. How much of a role do genes play? The environment -- peers, parents, educational efforts? What about the "gateway theory," the idea that one drug -- marijuana is the most likely to be blamed -- leads to use of others?

A new study of twins recently published online by the journal Drug and Alcohol Dependence suggests that genes may play a large role, but to some degree every drug is a gateway drug.

By studying both fraternal and identical twins (in this case, they focused on African-American teen girls, a population underrepresented in prior studies), researchers can set up mathematical models designed to probe the influence of environment and genetics. Focusing on alcohol, cigarettes, and marijuana, they found that early use either of alcohol or cigarettes was associated with an increased likelihood of being an early marijuana user, and early drinking was also associated with early cigarette use.  In general, those who had never used a given substance were the least likely to report having used the others -- so in a sense, almost any drug teens try seems to be a gateway drug.

Even more interesting, though, is the more detailed number crunching designed to tease out genetic vs. environmental influences. Inherited influences explained 44% of the variance in initiation of alcohol, 62% for cigarettes, and 77% of the variation in marijuana initiation. Because the confidence intervals (statistical-speak for margin of error) were fairly wide, those numbers should not be taken as gospel, but clearly genes play a major role in susceptibility to early substance use.

There is little doubt that some kids are innately more susceptible to early drug use than others. And a teen who tries one drug -- whatever it is, legal or illegal -- is more likely than his or her peers to try others. These are real issues that parents and educators need to face, and simplistically blaming marijuana as "the gateway drug" won't help them.

Okay, I'm a bit behind on my reading, but this is worth mentioning even though it's a little late. In its December issue, the American Journal of Public Health published the final, officially sanctioned evaluation of the anti-marijuana ads that former drug czar John Walters bombarded us with during the first half of the Bush administration (the evaluation period ends in June 2004). The bottom line: "[T]he campaign is unlikely to have had favorable effects on youths and may have had delayed unfavorable effects."

Translation: The ads didn't help, and may have actually encouraged teens to try marijuana.

The researchers drew this conclusion by measuring the marijuana-related attitudes and behaviors of thousands of teens before and after seeing the ads and correlating that behavior with their level of exposure to the campaign. There was simply no sign of a positive effect. And, though the results were somewhat inconsistent, several measurements connected increased exposure to the ads with development of pro-marijuana attitudes and increased likelihood of trying marijuana.

The drug czar's office hated this evaluation, conducted by the University of Pennsylvania and a private firm called Westat. Indeed, they kept it bottled up long after it should have been released. Then, when Congress got hold of it a couple years ago, they tried to dismiss it. Spokesman Tom Riley insisted to Adweek magazine that a reported general decline in teen marijuana use was proof of the campaign's success, saying, "The most telling statistic is that adult drug use has not appreciably changed while teen drug use [the target of the campaign] has gone down dramatically. I think that's the definition of successful advertising."

But the researchers easily shred such claims, noting that a great many other factors could have influenced use rates. As evidence, they cite "even larger declines in both tobacco and alcohol use than in marijuana use" that occurred at the same time, "suggesting that all substance use was on a downward trend regardless of the campaign."

So why did the anti-marijuana ads flop so badly? The researchers suggest two possibilities: The youthful tendency to rebel against adults telling them what not to do, and the possibility that the ads caused teens to think marijuana use is commonplace.

Here's another one: Walters' ads were so preposterous (some suggested that smoking marijuana will lead to shooting your friends or running over little girls on bicycles) that they caused young people to disbelieve the anti-marijuana message entirely. MPP will keep saying this until someone listens: Lying to kids about marijuana doesn't work.

MPP-TV just released this excellent video highlighting the need to tax and regulate marijuana. This piece is especially relevant now that California is considering groundbreaking reform legislation that has triggered a national discussion about the wisdom of marijuana prohibition.

Last Friday I had the opportunity to meet Glenn Greenwald, the best-selling author and Salon contributor who was presenting his report – funded by the Cato Institute – on Portugal's experience decriminalizing personal possession of drugs over the past eight years.

Few, even in the drug policy world, have paid much attention to Portugal's remarkable but sensible 2001 decision to remove drug use and possession from the criminal realm and address it solely as a public health issue.

The details of Portugal's system are worth checking out, but basically Portugal, after careful, empirical study, concluded that criminalizing drug use was creating two barriers to introducing treatment to those who might need it. First, it diverted funds that ought to go to drug treatment to ineffective law enforcement efforts. Second, the threat of arrest naturally caused those who might seek treatment to avoid, rather than seek out help from government institutions.

Under the current system, those caught possessing a personal amount of drugs, including marijuana, are cited by police and required to appear before a three-person panel made up of legal and healthcare professionals within 72 hours. The panel then conducts an informal interview with the person to determine what, if any, treatment might be necessary.

Greenwald was careful to note that the policy change was not an ideological decision, nor was it seen by Portuguese officials as some sort of social experiment. Rather, it was viewed as a necessary fix to alarming increases in drug abuse in the late '90s.

The result, according to Greenwald's analysis of the data and countless interviews with Portuguese officials, law enforcement and clients, has been a hands-down success. Despite some initial fears, drug use and drug-related crime have not increased. In many important categories and demographics, 15- to 19-year-olds for example, drug use rates have actually decreased.

And, nearly eight years later, there's little enthusiasm at all, even among conservatives and law enforcement leadership, to go back to criminalizing personal drug use and possession.

Greenwald argues that there's no reason to think that there's anything about the conservative, largely Catholic country that would make its success with decriminalization unique. He also suggested that, in general, empirical evidence supporting reform might be far more persuasive for advocates than ideological arguments about personal freedom or limiting government intrusion in adults' private lives.

I agree with Greenwald, and the data supporting his conclusions about Portugal's success with decriminalization are compelling and undeniable. But some comments made by Dr. Peter Reuter, the University of Maryland criminology professor who played devil's advocate at Greenwald's presentation, served as a reminder that there's still an important ideological component to the argument for sensible marijuana policy reform.

Reuter agreed that the data show decriminalization clearly hasn't exacerbated the country's drug problem. But he said he was less convinced that it proves decriminalization has actually caused decreases in drug use and abuse, pointing out that drug use rates in certain categories, notably marijuana, have decreased in many countries in the past several years.

Reuter said he believes popular culture has a far greater influence over drug use rates than drug policies themselves, a belief supported by a 2008 World Health Organization comparative study of 17 countries' drug use rates and drug policies.

It also reminds me a little of the Bush drug czar office's flimsy claims that arresting millions and lying to children about the dangers of marijuana were to thank for small decreases in youth marijuana use in recent years. We've always been very careful to avoid jumping to conclusions about causality and have been vigilant in calling our opponents out when they get carried away, as they often do.

So, if the best we can say is that, despite the unsubstantiated fears of prohibitionists, decriminalizing marijuana doesn't increase marijuana use rates or marijuana related-crime, then we're still left with an ideological debate: Either you believe that marijuana is inherently evil and that stigmatizing its use by making users criminals is worthwhile despite being ineffective, or you believe our marijuana policies should be measured by their effectiveness and not by arbitrary standards of morality.

Either way, I think we win.

A look at some of the reasons why the United States should consider taxing and regulating marijuana for responsible adult use.

Hear from Illinois medical marijuana patients on why you should support SB 1381 & HB 2514.

Senator Jim Webb (D-Va.) introduced the National Criminal Justice Act of 2009 last week, an exciting piece of legislation that will create a commission to study, among other things, America’s war on drugs.

The commission will look broadly at criminal justice reforms, with an emphasis on reducing America's rising prison population (now the largest in the world per capita). Centered in that debate is the hard truth about America’s punitive drug laws. One-third of U.S. inmates are drug offenders, and many of them are in jail for possession, not sale or manufacture.

Senator Webb's legislation calls, specifically, for a close look at our drug laws, and his remarks before the Senate show a refreshingly honest approach to the issue:

The elephant in the bedroom in many discussions on the criminal justice system is the sharp increase in drug incarceration over the past three decades. In 1980, we had 41,000 drug offenders in prison; today we have more than 500,000, an increase of 1,200% … and a significant percentage of those incarcerated are for possession or nonviolent offenses.

Webb isn’t playing it safe. Many politicians like to skirt around the edges of criminal justice reform, pursuing incremental changes and avoiding politically risky topics. Webb’s critique, on the other hand, is fundamental.

MPP Director of Government Relations Aaron Houston breaks down his testimony to Congress on April 2, 2009.

The evidence continues to mount that cannabinoids -- the unique, active components in marijuana -- fight cancer. The latest such study , just published in the Journal of Clinical Investigation, shows that THC can kill glioma cells through a process known as autophagy. Gioma is a particularly deadly form of brain cancer that afflicts, among others, Sen. Edward M. Kennedy (D-Mass.).

The good news is that this study got a decent amount of media attention. The bad news is that much of the coverage lacked context or presented information in a confusing or misleading way. Case in point: the April 1 story from the Reuters wire service.

Reuters reporter Michael Kahn presents the finding as if it were something brand new, failing to note the extensive evidence accumulated since the 1970s that cannabinoids fight various types of tumors. It reports that "studies have suggested" that marijuana may cause cancer, omitting the fact that the largest, most well-controlled studies have found precisely the opposite.

And finally, in a warning of possible risks of cannabinoid drugs, the article hopelessly jumbles cannabinoids -- drugs like THC and its plant and synthetic cousins -- with drugs designed to block the CB1 receptor through which these substances operate, mistakenly referring to these CB1-blocking drugs as cannabinoids. In fact, they're more like anti-cannabinoids, and if anything the harmful effects of these CB1 blockers (increased rates of depression and anxiety, for example) reaffirm that cannabinoids often have good and helpful effects.

The journal Clinical EEG and Neuroscience has just published a review of the data on the effects of substance use on the developing brains of adolescents. The unmistakable conclusion: While heavy substance use of any kind is a really bad idea for teens, the damaging effects of alcohol are clearly worse than marijuana. The researchers write:

Abnormalities have been seen in brain structure volume, white matter quality, and activation to cognitive tasks, even in youth with as little as 1-2 years of heavy drinking and consumption levels of 20 drinks per month, especially if >4-5 drinks are consumed on a single occasion. Heavy marijuana users show some subtle anomalies too, but generally not the same degree of divergence from demographically similar non-using adolescents.

Strikingly, in a couple of studies, the damaging effects of binge drinking were less if the drinker also used marijuana, suggesting -- though not proving -- a possible protective effect in some circumstances. That's actually no shock, as the U.S. government holds a patent  on cannabinoids -- marijuana's unique, active components -- as neuroprotectants (substances that protect nerve and brain cells from damage).