How do the producers use symbolism in the motion picture, Trainspotting?

The baby's death symbolizes a profound change in Renton's life. After being dead hours or even days, the baby's body is eventually discovered; immediately, Renton's life and character are also altered. Soon afterward, his own collapsed body is discovered in the street and he is admitted to the hospital so that (like a baby) he can be cared for by his parents until he stops using. The combined forces of the baby's death, Renton's hospital stay and the drug withdrawal enabled by his parents' firm-handed help all motivate Renton to finally try to stop using heroin.

While the baby dies because of neglect, Renton thrives as he is cared for and begins to care for himself. Renton takes control of his own life and chooses to go to London to create a new existence for himself. When Renton makes his fresh start in London, he is essentially like a child with a clean slate and no past. After starting anew, Renton wavers from time to time and does help his friends with one final drug deal. However, in the long run, Renton steadfastly removes himself from a drug culture that would let an innocent child die of neglect or allow him to waste his own life being high.