Katy Perry jokes about Rihanna's marijuana use.

The 'Roar' hitmaker has laughed at her showbiz friend's inability to switch off and relax despite looking ''so fresh'' all the time.

Speaking to Elle Canada magazine, she said: ''I think that Rihanna always looks so fresh and I'm like, 'How do you do that? We all know how much pot you smoke! And you don't sleep because you're on Instagram at four o'clock in the morning!' ''

Katy noted she has her own way to de-stress, revealing she has started to learn ''Transcendental Meditation''.

She added: ''I make sure to give myself a break. I had to find that balance.

''But I learned this thing called Transcendental Meditation, which I do as much as I possibly can.

''It's 20 minutes and you're supposed to do it twice a day, but I only do it once every other day - but anyway, it works. People say you should work out 30 minutes a day - none of us works out 30 minutes a day!''

However, Katy's more subdued ways of living her life don't impress everyone - singer Courtney Love has blasted her for being boring.

She previously said: ''I'm gonna be honest, Katy Perry bores the s**t out of me. She's a nice girl, she just really bores me. You know, that hillbilly Miley Cyrus is sort of punk in a weird sex way.''