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I hope the study itself is a bit better than the article. I do not hold my breath, however, given the quotation and conclusions.

Countering a basic principle of American anti-drug policies, an independent U.S. study concluded on Monday that marijuana use does not lead teenagers to experiment with hard drugs like heroin or cocaine.

Nobody said that people progress to cocaine while they are still teenagers.

By focusing on teenagers, the study cannot generalize to other populations, such as that of 20-30 year-olds, for instance. This is called a threat to external validity.

"Marijuana is not a gateway drug. It's just the first thing kids often come across."

What kind of logic is that? It's like saying, "The engine of a car is not a simple mechanism. It's just something people use to get to work." The second sentence has nothing to do with the first.

Does logic always fail this author or only when he reports his results?

Morral said 50 percent of U.S. teenagers had access to marijuana by the age of 16, while the majority had no exposure to cocaine, heroin or hallucinogens until they were 20.

There you go: so there is such thing as time after all. Another blunder:

"To a certain extent we are diverting resources away from hard drug problems," he said. "Spending money on marijuana control may not be having downstream consequences on the use of hard drugs."

But his study is cross-sectional rather than longitudinal; he did not even gather evidence that may support or contradict this assertion.

People like this author would not survive a year in engineering or science. But in "social sciences," such people even get outside funding. It is they who report to you on even numbered years that coffee is bad for you and, respectively, on odd-numbered years that it is harmless.

What kind of logic is that? It's like saying, "The engine of a car is not a simple mechanism. It's just something people use to get to work." The second sentence has nothing to do with the first.

No it isn't. It speaks to the nature causal relationship. Take people who eat dessert. Did their meal lead them to (make them) eat the dessert, or did the meal just happen to come first.

Gateway drug theory says that MJ use will lead to harder drugs. The study just says that people who are going to use hard drugs are going to use hard drugs wether MJ is the first drug they come across or not. Get it?