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PHOENIX - Hunched over a microscope, Steve Cottrell peered at a bud from a plant that is increasingly used as medicine in Arizona and across the nation.

He pointed at a computer screen that glowed with a magnified image of the marijuana bud. The sample, the size of a quarter, was covered with powdery white bumps - a mold that was invisible to the naked eye.

Increasingly, medical-marijuana dispensaries and patients are turning to laboratories to evaluate medical-marijuana plants, identify potentially harmful substances and pinpoint the potency of plants and cannabis-infused products, from caramels and "cherry roll" candies to butter.

Cottrell, 42, and his company, AZ Med Testing, is one of a number of labs in the state that cater to the burgeoning medical-marijuana industry. The lab, located in a small office complex in north-central Phoenix, works with about a third of the state's 70-plus dispensaries, he says.

Many dispensaries market organically grown marijuana, an important selling point for patients with weak immune systems that can be further compromised if noxious elements are inhaled. Using high-tech instruments, Cottrell looks for mold, bacteria and fungus, which can weaken patients' respiratory systems. He also tests for pesticides that can degrade the nervous system. And he tests the medicine to determine the amount of active cannabinoids - including CBDs, CBG, THC and THCA - the chemicals responsible for many of the physical and psychological effects of marijuana.

READ THE FULL STORY HERE: http://www.usatoday.com/story/news/nation/2014/01/06/medical-marijuana-purity-laboratories/4336123/

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