Inclusion Criteria:
* Willing and able to provide informed consent (for 16 and 17 year olds: assent and parental/ legal guardian consent)
* Non- or light-smoker (\< 5 cigarettes a day)
* Ability to attend appointments in Oxford with reasonable travel costs
* Ability/ willingness to provide GP contact details
Exclusion Criteria:
* Past or present DSM-5 axis-I diagnosis (based on SCID results at screening), especially severe psychiatric illness or alcohol or substance dependence
* First-degree family member with severe psychiatric illness
* CNS-medication last 6 weeks (including as part of another study)
* Current blood pressure or other heart medication (especially aliskiren or beta blockers)
* Diagnosis of intravascular fluid depletion or dehydration
* Impaired kidney function (based on blood test at screening, cut-off 75 ml/min/1.73 m2)
* Significant hyperkalaemia (level\>=6mEq/L in the absence of sample haemolysis will be considered significant hyperkalaemia)
* Very low blood pressure (defined as repeated (at least three consecutive measurements) measures of blood pressure under standardised conditions where either the systolic or the diastolic blood pressure or both are below 90/50 mmHg (in accordance with established standard definitions: DOI 10.1186/s12887-016-0633-7))
* Body weight below 35kg (as the lower dose of 25mg of losartan only indicated from 35kg)
* Lifetime history of epilepsy or other neurological disease (e.g. ADHD, autism)
* Lifetime history of angioedema, renal artery stenosis, valvular heart disease, recurrent postural/ orthostatic hypotension
* Lifetime history ofsystemic infection, or clinically significant hepatic, cardiac, obstructive respiratory, renal, cerebrovascular, metabolic, endocrine or pulmonary disease or disorder which, in the opinion of the investigator, may either put the participants at risk because of participation in the study, or may influence the result of the study, or the participant's ability to participate in the study.
* Significant loss of hearing that is not corrected with a hearing device Insufficient written and/or spoken English skills
* Women: pregnancy, breast-feeding
