This study aims to determine if the addition of Sodium Benzoate and / or NAC to TAU will be acceptable and tolerable and result in overall improvement of symptoms, social and cognitive functioning in patients with early schizophrenia spectrum disorder.

Inclusion Criteria:

1. Male/Female patients aged between 18-35 years.
2. Diagnosis of schizophrenia confirmed by SCID interview meeting DSM-V criteria for schizophrenia, schizophreniform or schizoaffective psychosis.
3. Stable on medication for the past four weeks
4. In contact with mental health services
5. Within 5 years of diagnosis of psychotic illness
6. Able to demonstrate the capacity to provide informed consent as assessed by their own clinician
7. Able to complete the required evaluations and take oral medication.
8. Effective contraceptive precautions (either the use of barrier methods or the oral contraceptive pill) to be taken by women of child-bearing age. A negative pregnancy test will be required in order to meet inclusion criteria.

Exclusion Criteria:

1. Prior history of intolerance or serious side effects to Sodium Benzoate or N-acetylcystine.
2. Concomitant use of Ascorbic acid
3. Active substance abuse (except nicotine or caffeine) or dependence within the last three months according to DSM-V criteria.
4. Relevant CNS or other medical disorders.
5. Pregnant or breast feeding
6. Diagnosis of Moderate to Severe Learning Disability
7. Relevant current or past haematological, hepatic, renal, neurological or other medical disorder in the opinion of the principal investigator (PI) or the responsible clinician, that may interfere with the trial.

Double-blind placebo controlled trial