Lifetime Dependence Risk (%)

Of all the people who smoke pot, in other words, about 9 percent will become dependent. But of all the people who drink, about 16 percent will become alcoholics.

There are some major differences between pot and the other drugs, of course. Cocaine addiction tends to be explosive—users want to do it again right away. Marijuana dependence is more “insidious,” as one paper describes it. The chance of getting hooked if you smoke it for the first time after age 25 is essentially nil; dependence is far more likely for people who start as teens. The withdrawal symptoms for marijuana are also far less intense than those of, say, heroin. Nevertheless, many scientists say people who quit weed cold-turkey experience trouble sleeping, irritability, and anxiety.

But this is all based on the studies that were conducted during the age of prohibition. Historically, people haven’t been able to get marijuana easily, which skews the addiction statistics.

“A factor that is confounding is if it's legal or not,” says Nora Volkow, director of the National Institute on Drug Abuse.

If you were at a party, she explained, someone might offer you cigarettes for the first time. You might try one, and if you were over 18, you could buy cigarettes the next day from a gas station. But if someone at the same party offered you cocaine, you could not pick some up at 7-11 the following day. You might have to wait several days, or weeks, before you used cocaine again, and thus you’d be less likely to get hooked. Cocaine, therefore, might seem in the medical literature to be less addictive than it actually is.

In the states with legal recreational marijuana, pot is now more like cigarettes.

“I predict that the [marijuana dependence] numbers may go up once the drug is more available,” Volkow said. “One of my concerns is that the legalization will make it more available.”

I caught up with Volkow at TEDMED, where another drug researcher, Columbia psychiatrist Carl Hart, offered a very different take. Hart, who advocates for the decriminalization of all drugs, says research shows fewer people become dependent on drugs if they are given other options for recreation.

The idea that crack users who take one hit will get hooked, “comes from experiments conducted in the 1960s to 1970s,” he said in his TEDMED talk. “Laboratory animals, when given unlimited access to drugs like cocaine and methamphetamine, will repeatedly press a lever to receive intravenous injections of the drugs until it kills them."

In those studies, the animals' cages contained nothing other than the lever leading to the drug dispenser. But what happened when the animals were presented with an alternative, like a sexually receptive mate or a sweet treat?

“When given an option, animals do not self-administer drugs until death," Hart said. "The animals will often take a non-drug alternative over the drug."