As your parents will be only too happy to tell you, today’s marijuana is much stronger than what the last generation smoked. CBS News reports that lab tests show the potency of marijuana in Colorado, where is recreational use of pot is legal, has increased by a factor of three in the past generation.

A company called Charas Scientific was hired to test the potency of pot currently sold there. As Andy LaFrate, Ph.D., lab founder and director of research, explained in a video released by the American Chemical Society, “We’ve seen a big increase in marijuana potency compared to where it was 20 or 30 years ago. … 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% THC.”

To put this information in context: NBC News reminds us that our parents were likely smoking weed reefer with THC percentage of only 10%. But in the recent tests, some strains of Colorado pot reached up to 30% THC.

READ MORE: Ask a Scientist: Why Does Weed Make Me Paranoid?

What do higher levels (no pun intended) of THC mean, other than a greater propensity for late-night Ben & Jerry’s runs? It could result in a greater chance of an adverse reaction, such as paranoia, or even a greater chance of growing a dependency on marijuana.

One more disconcerting fact to know: the pot tested was also “dirtier” than researchers expected. As notes, “it is often contaminated with fungi, pesticides and heavy metals.” LaFrate blamed a “hippy kind of mentality,” as he put it, for assuming that all marijuana is grown safely and naturally.

Currently, Colorado does not require that marijuana being sold be tested for contaminants (Washington State requires testing for yeast mold, E. coli, and salmonella, among other things.) However, LaFrate, conceded, “”Like ourselves, this plant is living with bacteria that are essential to its survival. In terms of microbial contamination, it’s kind of hard to say what’s harmful and what’s not.”  Just something to keep in mind next time you toke, Coloradoans.

You can watch a cool video from Charas on how marijuana is tested for potency here:

READ MORE: Ask A Scientist: Does Marijuana Cause Memory Loss?