Autism spectrum disorder (ASD) affects 20–30% of adults with intellectual disability. This group are vulnerable to challenging behaviour and mental health problems.

To explore the extent to which ASD affects challenging behaviour among specialist mental health service users with intellectual disability.

To identify predictors of challenging behaviour among adults who have intellectual disability.

A cross-sectional study of 92 participants from a specialist mental health service for adults with intellectual disability in the UK. The presence/absence of ASD was confirmed using the Autism Diagnostic Observation Schedule. Challenging behaviour was assessed using the Developmental Behaviour Checklist (DBC).

Participants with ASD (N=48) had higher total DBC scores than those without ASD (N=44; mean=54.2 vs. 29.2). ASD, severity of intellectual disability, age, presence of psychiatric disorder and total number of needs were entered as independent variables into a linear regression. The model accounted for 51% of the variance and was statistically significant (F(5,91)=18.1, p<0.001). Presence of ASD and total number of needs were the only significant predictors of challenging behaviour. Presence of ASD had the highest standardised coefficient (β=0.56).

Participants with ASD had significantly higher levels of challenging behaviour than those without ASD. Challenging behaviour was also independently associated with total number of needs. Understanding which service users with intellectual disability have higher levels of challenging behaviour than others despite receiving psychiatric treatment, and the extent to which having ASD is a contributing factor, should inform the development of more effective services and lead to improved outcomes.

Lysergic acid diethylamide (LSD) is a potent serotonergic hallucinogen or psychedelic that modulates consciousness in a marked and novel way. This study sought to examine the acute and mid-term psychological effects of LSD in a controlled study.

A total of 20 healthy volunteers participated in this within-subjects study. Participants received LSD (75 µg, intravenously) on one occasion and placebo (saline, intravenously) on another, in a balanced order, with at least 2 weeks separating sessions. Acute subjective effects were measured using the Altered States of Consciousness questionnaire and the Psychotomimetic States Inventory (PSI). A measure of optimism (the Revised Life Orientation Test), the Revised NEO Personality Inventory, and the Peter's Delusions Inventory were issued at baseline and 2 weeks after each session.

LSD produced robust psychological effects; including heightened mood but also high scores on the PSI, an index of psychosis-like symptoms. Increased optimism and trait openness were observed 2 weeks after LSD (and not placebo) and there were no changes in delusional thinking.

The present findings reinforce the view that psychedelics elicit psychosis-like symptoms acutely yet improve psychological wellbeing in the mid to long term. It is proposed that acute alterations in mood are secondary to a more fundamental modulation in the quality of cognition, and that increased cognitive flexibility subsequent to serotonin 2A receptor (5-HT2AR) stimulation promotes emotional lability during intoxication and leaves a residue of ‘loosened cognition’ in the mid to long term that is conducive to improved psychological wellbeing.