Media and public criticism at the time release, and even to this day, condemned Trainspotting as a glorification of drug use, heroin in particular.
The film, which fits into the British Social Realism genre, developed in the 30's and 40's, revolves around Mark Renton, a young man growing up in a working class area of Edinburgh during the 80/90's. Like so many of his real life contemporaries he is disillusioned and cynical about the future faced with such socioeconomic deprivation.
The opening of the film sees Renton fleeing from persuers after a shoplifting spree, and talking about "Choosing life, a career, a family, a home." and many other materialistic posessions which society dictates we must strive for, but which Renton wants no part of. He would rather escape his downward spiralling life through taking drugs, mainly heroin, but practically anything which will give him a "buzz," and his friends.
With Edinburgh boasting such tourist attractions as high unemployment and one of the highest heroin and heroin related aids problems in Europe it's not surprising and is in fact iconographic in it's portrayal of Renton as a heroin addict. the fact that he is addicted to heroin and unemployed means that he has to turn to crime to feed his habit, as the film shows with Renton shoplifting, stealing from an old peoples home and even stealing from his own mother. This cannot be seen as glorification, but only as a representation of a lifestyle in which we as the audience are asked to make no moral judgement.
I can understand how Trainspotting could be considered as pro-heroin, as a quote from Renton early on in film, about the effect of heroin states "Take your best orgasm and multiply it by a thousand and you"re still nowhere near it." The suggestion is that the "buzz" is so intense and takes you to such a level of escapism that he doesn't have to face the realities of his meager existence.