The new and ever-changing strains of marijuana being grown legally in states where it’s allowed and in basements and backyard greenhouses are not what your mom and dad may have tried back in the day.

We’ve heard the narrative for quite some time: Today’s marijuana is much stronger than what used to be available. But there’s been little proof to back it up.

“There is nothing natural today about marijuana. It has been genetically manipulated and altered into a product that nature never created.”

A recent study from the United Kingdom, however, finds that the more potent pot is, the more likely a person who uses it will become dependent on it.

Researchers from University College London found that those who consumed “high-potency” marijuana were twice as likely to become dependent as those who used lower-potency forms of the drug. They presented their results at the International Early Psychosis Association meeting in Milan in October.

“This is not surprising,” said Dr. Timothy Huckaby, medical director of Orlando Recovery Center and a triple board-certified physician in Pain Medicine, Addiction Medicine, and Anesthesiology; he also serves as president of the Florida Society of Addiction Medicine. “We have seen this time and time again with other substances.”

Huckaby said that for thousands of years, the indigenous people of South America chewed coca leaves and drank coca tea and did not have substance abuse problems because the bioavailability was low and the potency was low.

Related: Our Littlest, Most Vulnerable Ones are Going to Pot

“But when we were able to isolate cocaine, then refine it into a very high bioavailable product like crack cocaine, we saw epidemic problems with dependence and destruction. We are seeing this now with the high-potency heroin on the streets and the escalation to even more potent opioids like fentanyl, and high potency design opioids like W 18,” Huckaby told LifeZette.

He said he hears people all the time say, “Hey, it’s marijuana, it’s a natural product! It’s harmless.”

[lz_bulleted_list title=”Marijuana Measures Across U.S.” source=”http://www.drugpolicy.org”]Recreational use is on the ballot in Arizona, California, Maine, Massachusetts, and Nevada.|Medicinal use is on the ballot in Arkansas, Florida, Montana, and North Dakota.[/lz_bulleted_list]

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It makes him cringe.

“There is nothing natural today about marijuana. It has been genetically manipulated and altered into a product that nature never created,” he said. “The natural cannabis that nature created has a THC content of 1 to 2 percent. All prior statistics and studies about cannabis were done with a low-potency product that had a THC content of under 15 percent. Now we have oil extracts pushing the 90 to 95 percent THC limits. They can be smoked in a vaporizer and produce an effect on the brain that is unknown and understudied. Now, edibles and extracts push the envelope in terms of THC purity — and as this recent study points out, the risks of dependence has increased,” Huckaby added.

People are considered dependent on marijuana if they experience withdrawal symptoms — such as irritability, mood and sleep problems, and decreased appetite — when they are not using the drug, according to the U.S. National Institute on Drug Abuse (NIDA). Huckaby said with the legalization of cannabis, we are going to see more and more people exploited and hurt because we’re allowing use of a product that is not what nature created, and is anything but harmless for our society.

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“Instead of ‘Big Tobacco’ disseminating the lies that tobacco is harmless, we now have ‘Big Cannabis’ preaching the same deceptive message as they line their pockets with money,” he said. “I am seeing more and more young people who cannot stop smoking this high-potency marijuana — to the point that it creates all of the same problems in their lives as any other addictive substance.”

He added, “The greedy and money-hungry cannabis industry attempts to justify and limit the truth about the damage it is causing by saying things like, ‘Well, at least no one ever died from cannabis.’ They conveniently overlook the thousands and thousands of people who died from heroin overdose, who started out smoking a non-natural, genetically engineered, high-potency product that profoundly and permanently altered their brain chemistry and forever changed the course of their lives.”