User blog comment:Willbachbakal/Singleplayer Enemies: Little Sister/@comment-175.139.62.248-20130901142228/@comment-75.36.143.17-20130910091050

Peoples tolerance can vary alot. Some dont get addicted easy. Others wouldnt get as many side effects (like the deformations or insanity) from using ADAM). The amount of use and mix of different Plasmids/Tonics  could also matter as well as the quality (later ones less crude or bootleg ones being worjse).  Ones which made more drastic changes  likewise (ie consumer grade stuuf in the adverts vs combat plasmids...).

The ADAM in your body eventually degrades and its function stops and your original genetics reassert themselves    ^The harmful side effects (including addiction) probably manifested themselves after prolonged use (or it would have frightened too many people to want to use it and Ryan could have declared them poison and a health hazard)