SEATTLE – As states across the country have legalized medical and recreational marijuana, each one has varying legal limits determining whether a driver is impaired by marijuana.

In some states, drivers are not allowed to have any detectable amount of marijuana in their systems. Washington, Colorado, Montana, Pennsylvania, Ohio and Nevada each have set specific numerical standards to establish when a driver is legally impaired by marijuana. Other states have not.

Law enforcement agencies and state toxicology labs normally test blood or urine samples to determine the amount of marijuana in the system of a driver suspected of being impaired.

Research on marijuana’s potential for medicinal use has been hampered for years by federal restrictions, even though nearly half of the states and the District of Columbia have legalized medical marijuana in some form.

$1.1 billion of the $1.4 billion that the National Institutes of Health spent on marijuana research from 2008 to 2014 went to study abuse and addiction. Only $297 million was spent on its effects on the brain and potential medical benefits for those suffering from conditions like chronic pain.

How scientists study the effects of marijuana on the brain is changing. Until recently marijuana research largely excluded tobacco users from its participant pool, but scientists at the Center for BrainHealth at The University of Texas at Dallas have found reason to abandon this practice, uncovering significant differences in the brains of individuals who use both tobacco and marijuana and the brains of those who only use marijuana.

Caught in the crossfire between state and federal law, dispensary owners in states that have legalized medical cannabis are finding their businesses raided and their products seized

ast month, emergency services were called to an explosion at New MexiCann Natural, a licensed medical marijuana dispensary in Santa Fe, New Mexico. Two employees were injured while making edible cannabis products: Aaron Smith, 28, and Nick Montoya, 29. They were airlifted to University of New Mexico Hospital’s Level 1 Trauma Center with third-degree burns from a presumed butane reaction.

The History of Marijuana in 4:20 by 4TT--a brand new YouTube network covering news, music, culture, and sports -- all in a pot friendly way.

The Carnegie-Knight News21 program, a national multi-university reporting initiative headquartered at Arizona State University’s Walter Cronkite School of Journalism and Mass Communication, released a major investigation Sunday into the issues surrounding the legalization of marijuana in America.

Twenty-seven students from 19 universities traveled to more than 23 states and interviewed hundreds of individuals to report and produce “America’s Weed Rush.” The project is at weedrush.news21.com.

Marijuana’s effects can vary from person to person, and scientists are not quite sure what to make of the common distinction users and growers make between cannabis sativa and cannabis indica.

As marijuana prohibition falls in one state after another, cannabis sales are shifting from street corners to storefronts as opportunists line up to cash in on what optimists say is the biggest investment opportunity since the dot-com boom of the turn of the century.

Investors of all varieties are starting to look at marijuana as less of a stoner’s fad and more of a serious business venture. The industry totaled $2.66 billion in U.S. sales in 2014, up 74 percent from $1.53 billion the year before, according to the ArcView Group, a cannabis industry investment network. Experts expect billions more in future growth from states where the drug remains illegal – for the time being.

Last month, emergency services were called to an explosion at New MexiCann Natural, a licensed medical marijuana dispensary in Santa Fe, New Mexico. Two employees were injured while making edible cannabis products: Aaron Smith, 28, and Nick Montoya, 29. They were airlifted to University of New Mexico Hospital’s Level 1 Trauma Center with third-degree burns from a presumed butane reaction.

PITTSBURGH — In room 716 of the Children's Hospital of Pittsburgh, 12-year-old Hannah Pallas is motionless, but for an occasional turn of her head and blink of her eyes, following a series of life-threatening seizures. On the same day, 5-year-old Sydney Michaels is down the hall in room 749, waiting to be discharged after 15 grand mal seizures within 36 hours.

Their mothers have known each other for years, though it's a hapless coincidence caused by their daughters' epilepsy that brings them to the pediatric unit on the same day.