HOUSTON -

"The more you know, the more you grow; the more you grow, the more you know." That's what the teenagers age 13 to 17 are chanting at the Odyssey House, a special drug rehab center for drug addicted youth run by The Cenikor Foundation in Houston.

What these kids all know is that marijuana, especially when abused by teenagers with developing brains, is a very destructive drug.

Yes, marijuana, the same drug recently getting all that publicity, the same drug just legalized in the state of Colorado and on its way to being legalized elsewhere.

According to Constance Phillips, a licensed chemical dependency counselor at Odyssey House, marijuana is expected to be the fastest-growing, most popular illegal drug on Houston high school campuses this coming school year.

Phillips calls marijuana "the killer of all motivation" kids have to succeed in school.

"Their interest in school declines, they don't want to do anything, they become lazy, they become uninterested in the activities they were interested in before," she said.

Sixteen-year-old "Brandon," who wished to remain anonymous, is an example of what marijuana can do to a teenager's mind.

"I lost motivation first of all and I became lazy so would start skipping school, what did I care, about anything, I was getting high," he said.

Brandon said he was getting high on marijuana while at school. He bought the marijuana in a school bathroom every day.

Once a star football player on the varsity team and a top student academically, Brandon said pot destroyed his drive to succeed in anything.

"The competitiveness in me just went away, like I didn't care about being the fastest or the strongest no more, I just cared about going to smoke, when was I going to smoke again?" he said.

Now in Senior Foundation's rehabilitation program at Odyssey House, a program that helps more than 300 teens every year, Brandon has a warning for parents.

"Watch your children for the signs that they're addicted to pot," he said.

What are those signs?

--Red, bloodshot eyes.
--Clothes that reek of smoke every day.
--Falling grades.
--Diminished interest in activities they used to be engaged in.

Brandon said 60 percent of his classmates are currently using marijuana at school.

He said marijuana is easy to get and cheap. In fact, he said on any given day there are at least 20 guys he can buy marijuana from for as little as $10 a bag.

Brandon said marijuana nearly destroyed everything because it destroyed his ambition.

The Odyssey House in Houston treats adolescents with drug dependency problems through a variety of programs.