With the increasing attention marijuana has been receiving lately, especially with the legalization in states like Colorado and Washington, it’s high time (heh) someone took a look at how pot has actually changed along the years . Now, a study conducted by Charas Scientific, one of a handful of labs certified to test the potency of marijuana in Colorado, we know that weed today is much stronger than it used to be.

“We’ve seen a big increase in marijuana potency compared to where it was 20 or 30 years ago,” lab founder and director of research Andy LaFrate, Ph.D., said in a video released by ACS. Based on testing in laboratory equipment, “I would say the average potency of marijuana has probably increased by a factor of at least three. We’re looking at average potencies right now of around 20 percent THC.”

A hybrid Cannabis strain (White Widow) flower coated with trichomes, which contain more THC than any other part of the plant. Image via Wikipedia.

Tetrahydrocannabinol (THC) is the main  psychoactive constituent (or cannabinoid) of cannabis. First isolated in 1964 THC potentially has numerous medical applications, but also seems to pose health hazards (at least with heavy consumption). It’s not clear how the increase in potency affects the medical potential or health hazards. Higher concentrations of THC can have unpredicted results, for better or for worse. The increase is significant.

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“As far as potency goes, it’s been surprising how strong a lot of the marijuana is,” LaFrate said of the samples his lab has tested in recent months. “We’ve seen potency values close to 30 percent THC, which is huge.”

According to the institute, the potency of marijuana has been steadily growing for the past few decades. They said that as of 2012, marijuana confiscated by police agencies nationwide had an average THC concentration of about 15 percent, up from about 4 percent in the 1980s.

THC concentrations were likely manipulated by growers through cross breeding. The process of cross-breeding may also be responsible for another change in the makeup of some of the marijuana tested by Charas Scientific – the reduction of cannabidiol. Many samples turned out to contain little or no cannabidiol, or CBD, the compound responsible for most medical uses.

Another startling find was the discovery of contaminants in numerous samples – both biological and chemical.

“It’s pretty startling just how dirty a lot of this stuff is,” LaFrate said. Some plants turned out to be harboring fungi or bacteria. “It’s a natural product,” he said. “There’s going to be microbial growth on it no matter what you do. So the questions become: What’s a safe threshold? And which contaminants do we need to be concerned about?”

Previous testing at another Colorado lab, reported by CBS News last year, found mold, mildew, E. coli and salmonella in some marijuana.