Billy Connolly has warned budding stand-up comedians about the dangers of alcohol and drugs in the industry.
The Big Yin told how he risked his own career by drinking too much after shows and advised young comics to steer clear.
Connolly, 79, who is suffering from Parkinson's disease, has launched online comedy masterclasses on the BBC Maestro service where he shares wisdom from his 50-year career.
The Glasgow-born star said performing or writing material while under the influence never works and affects "sharpness, judgement and insight."
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He said: "Drugs and alcohol should be avoided if you're going to be a good comedian. It seems like a great idea at the time and it feels like a great idea.
"Where there's comedy, there's drink and drugs. It's nowhere near as bad as it used to be, but comedy is part of the night-time economy, and so is booze.
"Good comedians need to have confidence when they're on stage. Alcohol and drugs feel like shortcuts to achieving the confidence you need to stand in front of people and make them laugh, but it's always a mistake.
"The false confidence you get from being wasted comes at the price of sharpness, judgement and insight. The confidence is worth nothing because you're robbed of the other vital components you need to be excellent at comedy.
"As tempting as it might seem, a drink before performing is a waste of all the effort you spent getting this gig, preparing for it, all the stage-time leading to this moment for you to be the best you've been so far. It's just not worth it.
"Things sound good when you're drunk or stoned. You say things that sound very funny and especially to you. You'll be pissing yourself laughing. They're not as funny as you think most of the time.
"I've never met anybody that made drink and drugs an essential part of their lives who was a winner. It's a road paved with losers.
"It will make your material horrible, you'll do it all wrong and you'll think you have done great."
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In the course, Connolly tells how his wife Pamela Stephenson helped him to quit drinking and said he had her to thank for his longevity in show business.
He said: "I've never been drunk on stage. I've never been stoned on stage. But I've been drunk and stoned when I wasn't on stage.
"I used to be out of control. My roadie would be standing off stage with a gin and tonic and a cigarette and I would say 'Thank you ladies and gentlemen,' and walk right into it.
"If you enjoy a drink, having one after you've had a good gig can be fantastic. The difficulties start when the drink becomes the beginning of a night out; and that night out starts happening after every gig.
"You have to settle down or you won't last. My wife made me do it. She said 'Take it easy, you're burning out.'"
Connolly has joined other creative figures including Take That star Gary Barlow, actress Helena Bonham Carter and Line of Duty creator on BBC Maestro.
Each course costs £80 and has hours of content broken down into lessons ranging from 20 to 40 minutes, accompanied by course notes. Connolly announced his retirement from stand-up in 2018 but has continued to work on other projects.
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