brayden travis , from st charles county , missouri , has battled drug addiction since he was 15 and overdosed on heroin in early march .
the 18-year-old was left without medical attention for seven hours and suffered a stroke and severe brain damage .
doctors told his parents he might be left in a vegetative state but he is now conscious and has made small improvements .
his mother shared a photo of him in hospital in a bid to deter others from taking drugs ; the post has been shared more than 337,000 times .