Barratt 1997.

Methods	Design: placebo‐controlled cross‐over trial
Participants	Participants: male prisoners with recurrent aggressive behaviour Sex: male only Age: adults; age not reported Unit of allocation: individual participant Number randomised: 150 Number completing: 126; results reported for 60 (30 with primarily impulsive aggression and 30 with primarily premeditated aggression; remaining 66 had committed mixed types of aggression and were not included) (see note 2) Setting: prisons (number not reported); USA (Texas) Inclusion criteria: at least 3 documented aggressive acts (see note 1) committed while in prison in the 3 months preceding entry to the study Exclusion criteria: IQ less than 80; presence of DSM‐III‐R Axis I disorder as measured with PDI‐R; taking medication; presence of neurological or other serious medical disorder; presence of 'medical aggression' Ethnicity: not reported Baseline characteristics: aggressive behaviours preceded incarceration (98%); DSM‐III‐R antisocial PD (100%); lifetime, but not current, drug abuse problem (55%)
Interventions	Two conditions: phenytoin / placebo  phenytoin 300 mg/day, as 200 mg am and 100 mg pm placebo no further details reported Duration of intervention: 6 weeks Duration of trial: 13 weeks (cross‐over trial; 2 phases, 1‐week washout period between phases) Length of follow up: participants were not followed up beyond the end of the intervention period Dose adjustment: not reported
Outcomes	Primary outcomes Aggression (observer‐reported): intensity of aggressive acts (Overt Aggression Scale); frequency of aggressive acts Secondary outcomes Hostility: Profile of Mood States anger‐hostility subscale scores
Notes	1. Aggressive acts as defined in the handbook prepared by the Texas Department of Criminal Justice given to all prisoners 2. Aggressive acts classified as impulsive or non‐impulsive based on brief semi‐structured interview and written prison reports. An impulsive aggressive act defined as: "a 'hair‐trigger' non premeditated response to a stimulus that results in an immediate aggressive act or an agitated state that culminates in an aggressive act”.
Risk of bias
Bias	Authors' judgement	Support for judgement
Adequate sequence generation?	Unclear risk	Investigators report that participants “were randomly assigned to an initial drug/placebo condition” (p.3) suggesting that the order of treatments was randomised in this cross‐over trial. No further details reported. Clarification about method of sequence generation has been requested from the trial investigators, but no further information was available at the time this review was prepared.
Allocation concealment?	Unclear risk	No details reported. Clarification has been requested from the trial investigators, but no further information was available at the time this review was prepared.
Blinding? of participants	Unclear risk	Investigators describe the study as “double‐blind”. No further details reported. Clarification has been requested from the trial investigators, but no further information was available at the time this review was prepared.
Blinding? of personnel	Unclear risk	Investigators describe the study as “double‐blind”. No further details reported. Clarification has been requested from the trial investigators, but no further information was available at the time this review was prepared.
Blinding? of outcome assessors	Unclear risk	Investigators describe the study as “double‐blind”. No further details reported. Clarification has been requested from the trial investigators, but no further information was available at the time this review was prepared.
Incomplete outcome data addressed? All outcomes	Unclear risk	Insufficient reporting of attrition to permit judgement of ‘Yes’ or ‘No’. Appears that 24 did not complete study. A subgroup of 66 participants with 'mixed' type of aggression was excluded by investigators. Clarification has been requested from the trial investigators but no further information was available at the time this review was prepared. In this review, data from the subgroup of 60 completers were included in the analysis.
Free of selective reporting?	Low risk	Study protocol is not available but it seems clear that the published report includes all expected outcomes.
Free of other bias?	Unclear risk	There was a 1‐week placebo washout period between phases in this cross‐over trial. Trial investigators report no significant cross‐over effects for the aggression measures for the combined groups suggesting the study was not biased by carry‐over effects. However, of 150 randomised, results reported for only 60 of 126 completers (30 of which committed primarily impulsive and 30 of which committed primarily premeditated aggression; the remaining 66 had committed mixed types of aggression and were not included). Thus there is the possibility of bias through excluding the ‘mixed aggression’ group, although it is unclear what effect this would have on the results.