The 76-year-old comedian had decided to start using the drug to help him manage his incurable condition, which leaves him shaking and struggling to move.
However, speaking to the Radio Times, Billy admitted things hadn’t gone quite to plan.
“I just got bomb happy. Just stoned,” he said. “It was quite pleasant, but I don’t want to do that every day.
“I was never very good with marijuana, I always got too stoned and it always lasted too long. I stopped all that about 30 years ago.”
The Scottish comedian was diagnosed with Parkinson’s, along with deafness and prostate cancer, in 2013.
His wife, Pamela Stephenson, was forced to speak out about fears for his health earlier this year, when Billy’s friend Sir Michael Parkinson claimed he had taken a turn for the worse following a “sad and awkward” dinner he shared with Billy in 2016.
Addressing Michael’s comments in the Radio Times interview, Billy revealed he hasn’t spoken to his friend since he made the comments back in August.
“These Yorkshiremen, I don’t think they apologise much. I wasn’t disappointed, it just made my life a bit difficult,” he said.
“People feeling sorry for me, I don’t like that. They read about me in the papers and think, ‘Oh, he’s not well.’
“They’re right, but I’m not as bad as they think I am... He should get on with selling funerals and leave me alone.”
In recent years, Billy has spoken frankly about his battle with Parkinson’s disease, telling the Mail that a “sense of humour is absolutely essential” last year.
“It’s the only thing that gets you through,” he said.
“Sometimes I get kind of dark about it. It’s because it’s forever, you know. It’s not like having pneumonia and you’re going to get better. You’re not going to get any better.”
The full interview with Billy appears in this week’s Radio Times, on sale now.