NEW YORK ( MainStreet) — A Libertarian pot advocate turned opponent, Dr. Christian Thurstone, is at ground zero in the marijuana legalization battle. The medical director of a large Colorado youth drug treatment clinic; an associate professor of psychiatry at the University of Colorado, Denver; and one of a small number of doctors board certified in general, child and adolescent and addictions psychiatry, he has unique insight into the marijuana momentum sweeping the nation.

Thurstone believes that marijuana legalization is a disaster in the making. He is not shy about saying so. His experience with Colorado toe-in-the-water legalization of marijuana for medical purposes was his epiphany.

He noticed back in 2009, when Colorado began providing "medical" marijuana for its residents, that his clinic's clientele tripled: 95% of his patients came for marijuana addiction. He learned from his teenage clients that "medical" marijuana was easy to score on the streets. But the potency was increasing from medical grade. Soon his young clients would tell him how marijuana was their preferred medicine for relieving stress and anxiety.

Eventually, these young addicts came in with "medical" marijuana licenses. It was at this point Thurstone felt he needed to act. He wrote a piece for the Denver Post criticizing medical marijuana laws in January 2010 titled "Smoke and Mirrors: Colorado Teenagers and Marijuana."

Thurstone made some fighting points. "What Colorado has created is a backdoor way to legalize marijuana, and it has done so in a manner that makes a mockery of responsible medicine," he wrote.

He elaborated on this point by writing: "Let's stop talking in terms of smoked marijuana's medicinal value because we're not even close to knowing what that is. Let's instead answer the question that's truly at the heart of all of this political wrangling: Is smoking marijuana a civil right? Before answering that question, Colorado should carefully study the social costs of accidents, aggression, school dropouts, STDs and teen pregnancy that will inevitably be the result of increased marijuana use."

Five years later Thurstone continues his crusade. During an interview on Denver's KUSA television station in January, Thurstone was quoted as saying, "We're seeing a lot more patients, a lot more youth coming to treatment for marijuana addiction....If somebody tries marijuana before the age of 18, one in six develops an addiction to the drug. If someone waits until after 18, the number is more like one in nine."

"We have good reason to believe from both animal and human studies that exposure to marijuana during this important time of brain development can permanently change the way the brain develops," he added. "We have good evidence showing that marijuana exposure in adolescents confers up to an eight-point drop in IQ from age 13 to 38. We know that youth who use marijuana are two times more likely to develop psychosis as young adults."