Melissa Etheridge was returning to the United States from Canada in North Dakota when her tour bus was stopped by Customs and Border Patrol

Melissa Etheridge — a passionate advocate for medical marijuana — was busted for drug possession in August.

The 56-year-old singer was returning to the United States from Canada in North Dakota when her tour bus was reportedly stopped by Customs and Border Patrol. After drug-sniffing dogs detected the substance, agents discovered marijuana oil, according to TMZ.

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Etheridge told police that she uses the drug to manage pain from cancer. Although the drug is legal in California, however, it’s not allowed in North Dakota, said TMZ.

The “Come to My Window” crooner was reportedly booked for possession of a controlled substance and smiled from ear-to-ear in her mugshot, which was obtained by TMZ. According to the outlet, she pleaded not guilty. PEOPLE’s requests for comment were not immediately returned by CBP or a rep for Etheridge.

Etheridge first opened up about her weed use in the new Yahoo! project Cannabis & the American Family, and PEOPLE premiered the video clip earlier this year. The Grammy-winner explained that she began using medical marijuana as a holistic alternative to pharmaceuticals when she was undergoing chemotherapy after her 2004 breast cancer diagnosis.

During the initial interview, she added that she has smoked with her wife, Linda Wallem, and two older kids: Bailey, 20, and Beckett, 18. “It’s a very natural, end-of-the-day [thing],” she told Yahoo! “And it brings you much closer. I’d much rather have a smoke with my grown kids than a drink — oh, God, no.”

Since her quotes made the rounds online, Etheridge said she’s received flak for her parenting style and would hope the attention would be directed to a more important issue.

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Etheridge later clarified her comments exclusively to PEOPLE.

“I’ve been a celebrity here for almost 30 years, and I’ve done my best to speak truthfully about who I am and my human experience as I go through life, from my work to my family,” the rocker said. “Sometimes I find that I can say something, thinking that the whole world will understand, and they kind of go in another direction. I think if I get a little more specific, it can help guide the conversation in general about cannabis.”

Etheridge discussed why she believes her use of cannabis with her children has been “demonized” — and opened up about how heartbroken she was over the backlash she received for smoking with her kids.