WASHINGTON — (CNN) More than two years after Colorado began selling marijuana for recreational use, cannabis consumers have access to pot that sis more potent than ever.

There are dozens, if not hundreds, of different strains among thousands of plants grown legally under bright lights and fans in giant warehouses across the state.

“I think we’re the best industrial growers of cannabis in the world,” Medicine Man Marijuana CEO Andy Williams said of his company.

Williams owns a high-tech cannabis grow facility. He gave CNN a glimpse inside one section of it: a 12,000-square foot operation with machines that regulate temperature and humidity, and filter the air to create the best environment for fine-tuning cannabis concoctions.

“While we don’t do genetic engineering here, we’re constantly looking for better genetics. That means good, big and fast. So, it’s been a constant evolution of our genetics over time,” Williams said.

Canna Tsu, Cookies and Cream, Purple Dream and Screaming Gorilla are among the 50 to 60 different strains grown by Medicine Man. Levels of THC, marijuana’s psychoactive component, vary from strain to strain, ranging from 6% THC in Canna Tsu to 28% THC content in Williams’ Screaming Gorilla.

“It’s one product that’s fairly old-fashioned, compared to the hundreds that all these manufacturers and growers in Colorado are currently creating,” said Dr. Kari Franson, a clinical pharmacologist and pharmacist and the University of Colorado Skaggs School of Pharmacy. “They’re kind of creating a Frankenstein cannabis.”

In 2012, Colorado and Washington became the first states to legalize recreational marijuana, with Colorado implementing it first.

There are currently no regulations in Colorado limiting THC levels.

Earlier this year, some Colorado state legislators proposed an amendment to limit THC to 16% in marijuana and marijuana products sold in the state.

Proponents expressed concerns about the effects of THC on adolescent brains, among other health and safety issues.

But their effort to set a THC-limit failed to get enough support. Marijuana industry insiders say setting a limit could fuel the black market.

Williams likened it to the end of prohibition of alcohol.

“Those types of actions would be similar to saying we can’t have alcohol on the shelf other than beer, and people who don’t like beer, that want spirits, that want wine, are going to have to make it themselves,” Williams said.

Colorado state regulators do require recreational marijuana be tested for potency at third-party state licensed laboratories for labeling.

“The biggest issue is protecting the public’s health and safety and making sure this industry is based on sound accurate science,” said JJ Slatkin, director of business development at TEQ Analytical Laboratories.

TEQ has tested more than 100 different strains from more than two dozen clients, Slatkin said. His lab tests marijuana flower, concentrates and pot-infused products such as edibles.

While the tests measure potency of five different cannabinoids or components of the plant, THC is the cannabinoid connected to making people feel “high.”

Slatkin pulled up a recent test report showing a flower with about 32% total THC, acknowledging that it’s one of the highest THC levels he had seen in tests at TEQ.

CMT Laboratories, another state-licensed testing facility, reported test results with THC content as high as 28%.

In states where marijuana is still illegal, “they’re only growing or getting access to kind of low-grade marijuana,” said Franson.

Nationwide the average THC content found in confiscated marijuana has dramatically increased in just the last couple of decades.

“In the early 1990s, the average THC content in confiscated cannabis samples was roughly 3.7% for marijuana,” according to the NIH National Institute on Drug Abuse.

“In 2013, it was 9.6%.”

Another study that analyzed samples from pot seized by the US Drug Enforcement Administration from 1995 to 2014 also showed an increase in potency of “illicit cannabis plant material” from 4% THC content in 1995 to 12% in 2014, which is still far below what marijuana testing facilities are finding in Colorado and other states where recreational marijuana is sold.

These increasingly potent strains hit inexperienced users hard.

For Colorado residents, marijuana-related ER visits rose from 70 per 10,000 in 2012 to 101 per 10,000 in 2014 — a 44% increase.

While those numbers can’t be attributed solely to highly potent pot, Franson believes that’s part of it “for those few who unfortunately take too much in and have an adverse affect.”

“These people are getting so anxious and uncomfortable with how they feel. They sometimes have a feeling of impending doom and they’re like, ‘Oh my gosh, I’m going to die,’ so they go to the emergency room and seek assistance,” Franson said.

Marijuana users can also build a tolerance to THC. So higher potency can become necessary to achieve the desired effect over time, according to medical experts.

However, Williams said THC potency is not the only focus for growers or consumers. Some people use pot to help relax, for pain relief, even to help energize.

Different components of the marijuana plant can have different impacts.

For example, Williams said some of his customers prefer a pot product with higher concentrations of CBD, another cannabinoid, believed to help treat epilepsy and other serious conditions.

Williams said he remains focused on growing the best variety to meet different needs.

“Having that range of products that has great flavor, that has great effect, that’s repeatable and consistent for our consumers is what our goal is,” said Williams.