"He had experimented with cannabis several months prior, and when we had discovered that, obviously we came down very firmly, we had a zero-tolerance," Dr. Laura Berman says of her late son, Sammy

Dr. Laura Berman says she and her husband were "regularly" testing their 16-year-old son, Sammy, for drugs prior to his fatal overdose earlier this month.

In a PEOPLE exclusive sneak peek at Tuesday's episode of The Dr. Oz Show, Berman and her husband, Samuel Chapman, virtually sit down with Dr. Oz for an interview about their late son's experience with drugs, sharing that before his death due to Xanax laced with deadly fentanyl, he "had never done anything beyond" cannabis.

"Did you have any inclination that he might have started experimenting with drugs?" asks Dr. Oz, 60.

"No. He had experimented with cannabis several months prior, and when we had discovered that, obviously we came down very firmly, we had a zero-tolerance. We even got him a drug counselor that he met with and continued to," Berman, 51, who hosts In the Bedroom on OWN, the Oprah Winfrey Network, says of the teen.

"There was also a therapist that he met with once a week, we tested him regularly," she adds.

According to Berman, "there was a zero-tolerance in our house, and he had never done anything beyond that other than cannabis," she tells Dr. Oz.

Laura Berman
Dr. Laura Berman and her son Sammy
| Credit: Laura Berman/instagram

Berman announced the tragic news of her son's death to her followers Feb. 7 on Instagram. She revealed at the time that "a drug dealer connected with him on Snapchat and gave him [fentanyl] laced Xanax and he overdosed in his room."

As to how Sammy got a hold of the drugs, Berman believes her son obtained them from the drug dealer while he was either on a walk or when the family was sleeping.

"What we were able to piece together after the fact from his friends was that we believe that the toxicology reports will tell us exactly what he took, but that we believe it was probably he got it on Wednesday night. He took it on Sunday," she explains. "He just went outside either when we were sleeping or during the day maybe when he took a walk and he met this drug dealer that he had connected with on Snapchat, and got it that way."

In a statement to PEOPLE following news of Sammy's passing, a spokesperson for Snapchat said the company is "committed to working together with law enforcement in this case and in all instances where Snapchat is used for illegal purposes."

Laura Berman and Samuel Chapman
Samuel Chapman and Dr. Laura Berman; Dr. Oz
| Credit: ZoCo Productions, LLC

"We have zero tolerance for using Snapchat to buy or sell illegal drugs," the statement continued. "Using Snapchat for illegal purposes is firmly against our community guidelines and we enforce against these violations. We are constantly improving our technological capabilities to detect drug-related activity so that we can intervene proactively. … We have no higher priority than keeping Snapchat a safe environment and we will continue to invest in protecting our community."

The Centers for Disease Control and Prevention estimates that fentanyl, a rapid-acting opioid, is 80 times as potent as morphine and hundreds of times more potent than heroin.

Classified as a Schedule II drug by the federal government, its medical uses are typically pain management following surgery or for chronic pain.

Two days after Sammy's death, Berman and Chapman spoke out in the hopes of helping other parents.

"I didn't intend for us to be on the news, I just felt helpless," she told NBC News' Kate Snow on Today. "All I was thinking about is that this couldn't happen again and I was so furious and helpless." 

As for whether Sammy knew if the drugs he bought had fentanyl in them, his parents said "no way."

"Each different drug had a different color, the way a kid would love to see it," Chapman said of the "menu" Sammy used to purchase the drugs on the social media app.

If you or someone you know is struggling with addiction, please contact the SAMHSA substance abuse helpline at 1-800-662-HELP.