Possible Clues:

• Habit-forming
• Irresistible vice, dad troubled with it
• Irresistible supplement Charlie divides
• What food enhancer containing Charlie might be?
• Maybe colouring round first of copies proves compelling
• Maybe like harmful substance initially concealed in food preservative?
• (Of drug) habit-forming
• Extra cocaine is brought in - it being this?
• Hard to give up
• Cite David for causing compulsive or habit-forming behaviour