Inclusion Criteria:  A previous diagnosis of ADHD according to the DSM-IV or DSM-V criteria by a qualified health care professional. Children aged between 8 and 13 years at the time of study. Children with a comorbidity will be accepted. Both males and females  Exclusion Criteria:  Children currently undergoing a current course of behavioural therapy. Children currently on ADHD medication (such as methylphenidate) at the time of the study. Children with a reported milk allergy or lactose intolerance. Reported use of antibiotics, probiotics, antifungals or steroids in the past four weeks. Diagnosis of a gastrointestinal disorder e.g., Inflammatory Bowel Disease or Coeliac disease. Diagnosis of an auto-immune disease or compromised immunity.