Katy Perry takes pills to calm her nerves before her concerts.

The 29-year-old star - who is currently travelling the world on her 'Prismatic' tour - has admitted she has to self-medicate before going on stage because she doesn't want to let her fans down and give other singers the chance to take her place.

She said: "I have to take beta blockers, I get so nervous.

"I think I have to get through this; I can't let these people down, but mostly I can't let myself down. I've been given a great opportunity and there are 500 bitches behind me who will snatch my weave off my head if I don't kick-ball-change through this two-hour show.

"There is a lot of choice out there. All I'm trying to do is make great music."

Despite admitting to taking beta blockers, which can be used to treat anxiety, the 'Dark Horse' hitmaker claims she never mixes them with alcohol, and instead waits until a show is over before she indulges in a drink.

She told Cosmopolitan magazine: "I always have one [a drink] waiting for me when I get off stage - a glass of champagne."

Katy also confessed that champagne is now her alcoholic beverage of choice, as she can't handle spirits as well as she could when she was younger.

She added: "I definitely black out on whiskey so I don't drink it anymore.

"Champagne usually gives everybody a headache, but I can have, like, five glasses and be completely fine."