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Boys who smoked marijuana heavily were significantly smaller than their peers by the end of their adolescent growth phase, according to a study conducted in Pakistan.

Study participants who were described as "marijuana addicts" during boyhood were on average 4.6 inches shorter and 4 kg lighter at age 20 than nonsmokers, reported lead investigator Syed Shakeel Raza Rizvi, PhD, and colleagues at the , in a presentation at the in Dublin.

The investigators compared height; weight; and levels of luteinizing hormone, testosterone, growth hormone, and cortisol in 220 marijuana-addicted and 217 nonpot-smoking boys.

Plasma concentrations of luteinizing hormone, testosterone, and cortisol were significantly higher in the marijuana addicted boys, but levels of growth hormone were significantly lower.

Chronic pot smoking may trigger a stress response that stimulates the onset of puberty but lowers growth hormone levels, the researchers suggested, on the basis of a separate set of laboratory experiments.

To determine the acute effect of smoking marijuana on cortisol levels, the researchers measured salivary cortisol in 10 "drug addict volunteers" of unstated age before, during, and after smoking a 0.25 g marijuana cigarette. "Acute administration of marijuana induced significant increases in the salivary concentrations of cortisol," the researchers reported.

"The mechanism underlying the stimulation of reproductive function by marijuana in pubertal boys needs to be examined in detail. Furthermore, the suppressive effect of cortisol on growth directly through inhibition of growth at the cellular level by depletion of nutrients or indirectly through inhibition of growth hormone secretion needs to be further studied," Rizvi said via email to MedPage Today.

"In addition, it is to be ascertained whether cortisol itself or some other factor like nutritional status is attributable to decline in growth rate in pubertal marijuana addicted boys. We are examining these aspects currently," Rizvi said.

In the U.S., marijuana is the most popular drug among young people, with 11.7% of 8^th graders and 35.1% of 12^th graders reporting having used it within the past year, according to a

More than 6% of 8th graders and 21% of 12th graders reported using marijuana within the past month, the survey found, and about 1% and 6% of 8th and 12th graders, respectively, said they used the drug daily.

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