Inclusion Criteria:

1. Aged 18-65 years
2. Diagnoses of schizophrenia or schizoaffective disorder using the Diagnostic and Statistical Manual-IV (DSM-IV) criteria
3. Competent and willing to give informed consent
4. Able to take oral medication and likely to complete the required evaluations.
5. Medication remained stable 4 weeks prior to baseline.
6. Female participants of child bearing capability must be willing to use adequate contraceptives (4.6.1a) for the duration of the study, and, willing to have a pregnancy test pretreatment and during the study.

Adequate contraception is defined as use of contraceptive double barrier system (i.e. condom and spermicide) or contraceptive implant, oral contraceptive or injected depot contraceptive plus other form of contraceptive, i.e. condom. Females will be considered incapable of child bearing if they are one year postmenopausal or irreversibly surgically sterilised.

Exclusion Criteria:

• Relevant medical illness [serious renal, diabetes, hepatic, cardiac, low- or high-blood-pressure or other illnesses] in the opinion of the investigators. In particular, history of past or recent cardiac illness, MI and abnormal ECG and current treatments for cardiac illness. The results of the Laboratory Investigations (LFT, TFT, RFT, WBC, ECG, platelets, blood chemistry, lipids, weight/BMI) will be taken into account in determining the exclusion criteria.

  1. Relevant medical illness will be determined in the first instance by asking the patients mental health care team if the patient has any medical condition/problems. After consent has been obtained, the research nurse/research doctor will then have access to the patient's notes and if necessary communicate with his/her GP and will assess patient eligibility to take part in the clinical trial by scrutinising the patient's past medical history, most recent blood results, electrocardiograms, as well as any physical tests that have been performed on the patient. If there are any deviations from the 'norm' the investigators will assess the eligibility of the individual patient.
  2. Patients receiving active treatments for Herpes virus as L-arginine may counteract the benefits of lysine to treat herpes virus
  3. Patients who are currently receiving NSAIDs or other drugs that can cause significant stomach an gastrointestinal side-effects
  4. Drugs that alter potassium levels in the body, such as ACE inhibitors and potassium sparing diuretics
  5. Patients who are pregnant or plan to become pregnant while using this amino acid
  6. Patients who are breastfeeding
  7. Prior history of intolerance to L-arginine
  8. Any significant change of psychotropic medications done within the previous 4 weeks
  9. Diagnosis of substance abuse (except nicotine or caffeine) or dependence within the last three months according to DSM-IV criteria