NCT02940574.

Study characteristics
Methods	4‐week trial of oxytocin versus placebo
Participants	Inclusion criteria: clinical diagnosis of ASD, Asperger's Syndrome or Autism male aged 18‐40 years Exclusion criteria: associated neuro(psycho)logical disorder (i.e. epilepsy, concussion, stroke), eyesight worse than + or ‐ 7, Genetic syndrome, colour blindness any contraindication to neuroimaging research as assessed with the MRI screening list: pacemaker, implanted defibrillator, ear implant/a cochlear implant, insulin or implanted pump, a neurostimulator or ventriculoperitoneal shunt, any metallic object in the eyes (metallic fragments). Location/setting: Belgium Mean IQ: details not provided Mean age: 18‐40 year olds Gender: all participants were male. Sample size: 40 (oxytocin 22, placebo 18) Reasons for dropouts/withdrawals: 1 in oxytocin group withdrew from the study, 1 from placebo not included in analysis due to "excessive in‐scanner head motion" Baseline ABC‐I or other BoC scale: not an outcome Concomitant medications: details not provided Previous medications: details not provided
Interventions	Intervention (oxytocin) for 4 weeks: single dose of 24 IU oxytocin (Syntocinon) nasal spray (3 puffs of 4 IU per nostril), followed by 4 weeks of a daily single dose (24 IU; 3 puffs of 4 IU per nostril) of nasal spray. Comparator (placebo) for 4 weeks: placebo (physiological water (solution of sodium chloride (NaCl) in water)) administered via nasal spray. A single dose (24 IU) of nasal spray (3 puffs of 4 IU per nostril), followed by 4 weeks of a daily single dose (24 IU; 3 puffs of 4 IU per nostril) of nasal spray.
Outcomes	Primary outcomes: AEs Secondary outcomes: QoL, measured using the WHO‐QoL (WHO 1998) (higher scores indicate a more positive response) tolerability Timing of outcome assessments: baseline and 4 weeks (endpoint)
Notes	Study start date: October 2016 Study end date: February 2020 Funding: details not provided Conflicts of interest: details not provided
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Insufficient detail: "allocation: randomized"
Allocation concealment (selection bias)	Unclear risk	Insufficient detail. Quote: "allocation: randomised"
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Only details provided were on the trials registry Quote: "masking: quadruple (participant, care provider, investigator, outcomes assessor)"
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Only details provided were on the trials registry Quote: "masking: quadruple (participant, care provider, investigator, outcomes assessor)"
Incomplete outcome data (attrition bias) All outcomes	Low risk	Quote: "1 subject lost in Syntocinon group due to subject withdrawal. 1 subject lost in placebo group due to low data quality (excessive in‐scanner head motion)"
Selective reporting (reporting bias)	Unclear risk	Difficult to know without a protocol
Other bias	Low risk	No other apparent sources of bias