Robbie Williams has described marijuana as a "lovely drug", but said it "doesn't mix well with me".
The singer (36), who had a long battle with drink, drugs and depression, said that it was "a shame".
Referring to the tendency to binge-eat after smoking marijuana, Williams, whose song Morning Sun is this year's official charity track for Sport Relief, said: "Did you see me last year? Have a look at last year. Yep. Year of the Munchie 2009.
"Weed, it's such a lovely drug. It is such a lovely drug...but it doesn't mix well with me -- at all," he said.
"It doesn't take much to trigger -- I mean, I'll get psychosis from having this cup of tea! Seriously. The caffeine in that's enough. Yeah. A cup of tea will make me feel like s***.
"But it's just a shame about weed, because I did love it."
Chris Hudson, a nurse from drugs information service Frank, wouldn't comment on the former Take That star's remarks directly, but said: "Cannabis messes with your mind -- and reactions can be more powerful with stronger strains such as skunk, which is around twice as potent. Mental health problems associated with using cannabis include paranoia, panic attacks and anxiety and depression. The risks increase the more you use it."
Speaking of his last spell in rehab three years ago, Williams said: "I was dying. I got to the point where I really, genuinely didn't care. I'd just got fat and depressed before. Then this one was like, 'you might die'.
But he was "not at all" bothered by the prospect of dying, he said.