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Epidemiological studies have reported that the increased risk of developing psychosis in cannabis users is dose related. In addition, experimental research has shown that the active constituent of cannabis responsible for its psychotogenic effect is Delta-9-Tetrahydrocannabinol (THC) (Murray et al, 2007). Recent evidence has suggested an increased in potency (% TCH) in the cannabis seized in the UK (Potter et al, 2007).
We predicted that first episode psychosis patients are more likely to use higher potency cannabis and more frequently than controls.
We collected information concerning socio-demographic, clinical characteristics and cannabis use (age at first use, frequency, length of use, type of cannabis used) from a sample of 191 first-episode psychosis patients and 120 matched healthy volunteers. All were recruited as part of the Genetic and Psychosis (GAP) study which studied all patients who presented to the South London and Maudsley Trust.
There was no significant difference in the life-time prevalence of cannabis use or age at first use between cases and controls. However, cases were more likely to be regular users (p=0.05), to be current users (p=0.04) and to have smoked cannabis for longer (p=0.01). Among cannabis users, 86.8% of 1st Episode Psychosis Patients preferentially used Skunk/Sinsemilla compared to 27.7% of Controls. Only 13.2 % of 1st Episode psychosis Patients chose to use Resin/Hash compared to 76.3% of controls. The concentration of TCH in these in South East London, ranges between 8.5 and 14 % (Potter et al, 2007). Controls (47%) were more likely to use Hash (Resin) whose average TCH concentration is 3.4% (Potter et al, 2007).
Patients with first episode psychosis have smoked higher potency cannabis, for longer and with greater frequency, than healthy controls.
Why patients with psychosis use cannabis remains debated. The self-medication hypothesis has received some support but other evidence points towards an alleviation of dysphoria model. This study investigated the reasons for cannabis use in first-episode psychosis (FEP) and whether strength in their endorsement changed over time.
FEP inpatients and outpatients at the South London and Maudsley, Oxleas and Sussex NHS Trusts UK, who used cannabis, rated their motives at baseline (n = 69), 3 months (n = 29) and 12 months (n = 36). A random intercept model was used to test the change in strength of endorsement over the 12 months. Paired-sample t-tests assessed the differences in mean scores between the five subscales on the Reasons for Use Scale (enhancement, social motive, coping with unpleasant affect, conformity and acceptance and relief of positive symptoms and side effects), at each time-point.
Time had a significant effect on scores when controlling for reason; average scores on each subscale were higher at baseline than at 3 months and 12 months. At each time-point, patients endorsed ‘enhancement’ followed by ‘coping with unpleasant affect’ and ‘social motive’ more highly for their cannabis use than any other reason. ‘Conformity and acceptance’ followed closely. ‘Relief of positive symptoms and side effects’ was the least endorsed motive.
Patients endorsed their reasons for use at 3 months and 12 months less strongly than at baseline. Little support for the self-medication or alleviation of dysphoria models was found. Rather, patients rated ‘enhancement’ most highly for their cannabis use.
Cognitive impairment, particularly in memory and executive function, is a core feature of psychosis. Moreover, psychosis is characterized by a more prominent history of stress exposure, and by dysregulation of the hypothalamic–pituitary–adrenal (HPA) axis. In turn, stress exposure and abnormal levels of the main HPA axis hormone cortisol are associated with cognitive impairments in a variety of clinical and experimental samples; however, this association has never been examined in first-episode psychosis (FEP).
In this study, 30 FEP patients and 26 controls completed assessment of the HPA axis (cortisol awakening response and cortisol levels during the day), perceived stress, recent life events, history of childhood trauma, and cognitive function. The neuropsychological battery comprised general cognitive function, verbal and non-verbal memory, executive function, perception, visuospatial abilities, processing speed, and general knowledge.
Patients performed significantly worse on all cognitive domains compared to controls. In patients only, a more blunted cortisol awakening response (that is, more abnormal) was associated with a more severe deficit in verbal memory and processing speed. In controls only, higher levels of perceived stress and more recent life events were associated with a worse performance in executive function and perception and visuospatial abilities.
These data support a role for the HPA axis, as measured by cortisol awakening response, in modulating cognitive function in patients with psychosis; however, this association does not seem to be related to the increased exposure to psychosocial stressors described in these patients.
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