British pop star Robbie Williams has come under fire from anti-drugs campaigners for championing marijuana as a 'lovely' drug.

The 'Feel' hitmaker, who has struggled with substance abuse problems in the past, admitted he gained several pounds while smoking cannabis but branded the drug 'lovely', reports contactmusic.com.

'Weed, it's 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's enough. But it's just a shame about the weed, because I did love it,' he said.

Anti-drugs activist Debra Bell took exception to the remarks, insisting the singer's comments are irresponsible.

'Does he really know what he's saying? This drug causes huge damage to children and their families,' she said.