A follow-up documentary, The Boy Can't Help It, was aired by the BBC in 2002, catching up with Davidson, aged 30, to see how he continued to cope with the condition.
It also visits an 8 year old named Greg Storey, from Yorkshire who also has Tourette's, and offers his experience of it at an early age.
Both John's Not Mad and an edited version of The Boy Can't Help It omitting the scenes dealing with Greg Storey were released on DVD in 2006 with the proceeds going to the Tourette Scotland foundation.
[2] The documentary achieved a cult status soon after it was first aired and, contrary to the "possible good intentions of the film crew, it has been seen as some sort of comedy classic.
In May 2009, BBC television broadcast Tourettes: I Swear I Can't Help It, a follow-up to the 1989 and 2002 documentaries, that caught up with both John (at 37) and a 15-year-old Greg, to see how their lives had changed in seven years.