Miley Cyrus reveals the drug that prevented her from driving for three days.

While speaking with David Letterman, Miley revealed that her mom Tish Cyrus' weed is 'too heavy.'

Miley Cyrus reveals the drug that prevented her from driving for three days.

Miley Cyrus couldn’t handle one specific drug, which she revealed during the latest episode of My Next Guest Needs No Introduction With David Letterman. The Grammy Award winner, 31, recalled an incident when she couldn’t even drive for several days after taking “the smallest puff ever” of her mom Tish Cyrus‘ weed.

“I don’t smoke my mom’s weed anymore,” the “Flowers” artist admitted before explaining why. “The last time I smoked her weed was a couple weeks ago, and I did walk in and take the smallest puff ever. and I couldn’t drive for what felt, like, three days, and I didn’t know who I was.”

Although “usually” Miley will “fake it to be cool for [her] mom,” she pointed out that Tish “gave Wiz Khalifa a panic attack ’cause her weed was too heavy.”

“I will randomly take one small puff off my mom’s joint pretty much never because it’s way too strong,” she concluded.

As for what Tish, 57, said to Miley, the Disney Channel alum revealed that her mom once told her, “OK, but just don’t tell anybody ’cause I’m a good Christian woman.”

Tish appeared on the special with David Letterman as well. At one point, she remembered what her “biggest fear” was when Miley was growing up and skyrocketing to fame.

“Honestly, I think my biggest fear was her moving out,” Tish said. “She definitely had financial ways to be able to move out before she was 18, and you see that a lot with kids in Hollywood. But she didn’t. I think I really picked my battles with her.”

In addition to the Hannah Montana alum, Tish also shares Noah, Brandi, Trace and Braison Cyrus with ex-husband Billy Ray Cyrus.

During the special with David, Miley also opened up about her rumored estrangement from her dad, 62. While calling Tish her “hero,” the former Disney Channel star credited Billy with helping her as an artist. However, she noted that she “inherited the narcissism from [her] father.”