DENVER (CBS4) – The marijuana sold in Colorado dispensaries is exponentially stronger than what people smoked decades ago. Advances in technology and growing techniques have produced a more potent product.

According to a University of Mississippi study published in 2008, levels of THC, the active ingredient in marijuana, varied between 3 percent and 9 percent. Now, some of the strongest medical marijuana in Colorado has tested as high as 30 percent.

CBS4 was invited to tour Denver Relief’s grow operation at an undisclosed Denver warehouse. Workers showed how they babied the plants, playing music for stimulation and lightly touching the leaves to encourage root growth. Lighting and watering was meticulously monitored and grow cycles were timed down to the day.

Marijuana grower Nick Hice explained that today’s marijuana is much stronger than pot from previous generations. Unlike today’s carefully grown crop, marijuana of the past was typically grown outdoors in covert locations. What consumers got was a roll of the dice.

Hice says stronger marijuana gives the patient more value for their money.

“If we can get the same effect out of a smaller amount of product then it’s a win-win for everyone,” Hice said.

There is an arms race in the marijuana industry to keep coming up with stronger products.

“There are a lot of breeders out there and there are new strains coming out every day of the week, so it is kind of hard to keep up,” Hice said.

At Denver Relief and many other dispensaries, the most potent pot is often the most expensive. But Denver Relief is one of the few stores that lab tests its products so it can accurately inform its customers.

According to CannLabs, a local testing company, 85 percent of dispensaries don’t scientifically test their marijuana on a regular basis so they really don’t know the strength of the marijuana they sell.

“The good news is that if they have too much nothing is really going to happen,” said Denver Relief co-owner Ean Seeb. “They might lay down for 45 minutes to an hour and sleep, but nobody is going to overdose.”

But the potency race has had some unexpected side effects. Some merchants distill their plants into hash, a more concentrated, powerful, version of marijuana. Some hash made with butane tests at more than 90 percent THC. But when manufactured incorrectly, butane hash can be explosive. In 2009 a house exploded in Breckenridge sending two hash makers to the hospital.

After the incident in Breckenridge, Fire Marshal Jay Nelson with Red White and Blue Fire Department said the butane being used to extract the THC from the marijuana should never have been used inside the home.

“When butane is used indoors, severe injury or death may result,” explained Nelson.

Denver Relief co-owner Kayvan Khalatbari says butane hash is growing in popularity. He believes its safe when made by professionals.

“They are being idiots with it.” Khalatbari said. “We truly believe butane extraction used in the right methods is no more dangerous that using a lighter and smoking a bowl.”

California has banned the manufacturing of butane hash after a series of explosions there.