Closing this year’s Edinburgh International Film Festival, Paul Sng’s documentary about Irvine Welsh is themed around a ‘cosmic exploration’ of sorts. The Trainspotting author is filmed taking psychedelic hallucinogen DMT, using chemical enhancement to seek self-enlightenment in more clinical circumstances than the messy, drug-addled scenarios featured in his Rabelaisian novels. Dull reality doesn’t suffice for the combative Welsh, searching for new ways to have ‘a square-go with yourself’, but Sng’s documentary captures the author’s desire to chart his own inner psyche, a ‘psychoactive terrain’ illustrated here with writings read by Maxine Peake, Liam Neeson and others.

Providing insight into daily routines, Welsh is seen busy in the DJ booth or returning to his home turf playing five-a-side football, while boxing allows him to explore ‘different neural pathways’ in his head. Welsh is tackled about using drugs as part of his creative process, but all he can discern about his narcotic experimentation is the ancient truism that ‘you feel brilliant until you don’t’. After emerging from his DMT journey, Welsh murmurs ‘I don’t actually have the words for it’. But this nimble, incisive and questioning documentary does a far more accurate job of articulating how Irvine Welsh deals with reality, finding fresh routes to chase oblivion, still under the chemical cosh.

Reality Is Not Enough screened at Edinburgh International Film Festival, and is in cinemas from 26 September.