They also have fears it could influence children who use the social media site without any age controls. The letter, external-link which has support from parliamentarians and leading clinicians, says the group is 'distressed' to see this type of advertising, which is 'difficult for those of us who are addicted or in recovery'.
The adverts have also drawn criticism from some football supporters. They highlight how clubs offer match odds and links to betting sites when revealing starting line-ups on Twitter.