"Have a look at [me] last year. Yep. Year of the Munchie 2009," he told UK's Radio Times.
"Weed, it’s such a lovely drug. It is such a lovely drug. But it doesn’t mix well with me – at all.
"It doesn’t take much to trigger – I mean, I’ll get psychosis from having this cup of tea! Seriously. The caffeine in that is enough. A cup of tea will make me feel like s***. But it’s just a shame about weed, because I did love it."
Robbie has famously battled addiction to cocaine and prescription drugs, and has been rehab-free since 2007.
More reformed celebrity addicts in our gallery!