Cannabis is the world's most widely used illicit drug. It can impair verbal learning and induce psychosis, both acutely and possibly following long term use. But, where cannabis acts in the brain to impair verbal learning and induce psychotic symptoms is unclear. The aim of this study was to clarify how one of the main psychoactive ingredients of cannabis, delta-9-tetrahydrocannabinol (THC) acts on the brain to impair verbal learning and induce psychotic symptoms.

15 healthy males with minimal exposure to cannabis, were studied on 2 occasions approximately 1 month apart, following oral administration of 10mg of THC or placebo 1 hour prior to scanning, in a double-blind design. MR images were acquired on a 1.5T GE camera while subjects performed a Verbal paired associates task with separate encoding followed by retrieval conditions, with the conditions repeated in the same sequence 4 times. We examined the main effects of drug, task and drug- task interactions.

Administration of THC abolished the normal linear decrement in parahippocampal activation across successive encoding blocks and was associated with a trend for impaired word recall. Administration of THC also altered the normal time-dependent change in ventral striatal activation during retrieval of word pairs which was directly correlated with concurrently induced psychotic symptoms.

These results suggest that impairment in learning and verbal memory associated with cannabis use may be mediated through its action in the medial temporal cortex while psychotic symptoms may be induced through its action in the ventral striatum.

Cannabis has well established effects on cognitive processing but the neural basis of these is unclear. We used functional neuroimaging to investigate this, focusing on tasks that engaged verbal memory and response inhibition.

Subjects were 15 healthy males who had used cannabis < 25 times in their lifetime. Each subject was studied on 3 occasions, and was given either THC, CBD or placebo 1 hour prior to scanning, in a double-blind design. The order of drug administration was randomised and there was 1 month between each scanning session. During each session, images were acquired on a 1.5T GE camera while subjects performed a verbal paired associates memory task and a Go/No Go task. The modulatory effects of THC and CBD relative to placebo were examined by comparing activation during each task.

During the encoding phase of the memory task THC attenuated activation in the left temporal cortex compared to placebo. During the go-no go task, THC attenuated activation in the right inferior frontal cortex. Neither of these effects were attributable to differences in behavioural performance, sedation, or intoxication. The severity of psychotic symptoms provoked by THC was a function of its effect on right inferior frontal activation during response inhibition.

The effects of cannabis on verbal memory and motor control may be mediated through the influence of THC on left temporal and right inferior frontal activity, respectively. The induction of psychotic symptoms by cannabis may reflect an effect of THC on right inferior frontal activity.

The study sought to examine the neurophysiological effects of cannabidiol (CBD) on the emotional processing using functional Magnetic Resonance Imaging (fMRI).

Fifteen healthy male participants (age range 18-35) with a lifetime exposure to cannabis of 15 times or less were recruited in a double blind event-related fMRI design. Prior to each scanning session, participants were given an oral dose of either 600mg CBD or a placebo. The blood levels of drugs were monitored via an intravenous line, while systolic and diastolic blood pressure and heart rate (beats per minute) were recorded manually. During the scan, subjects were presented with 10 different facial identities, each identity expressing 50% or 100% intensities of fear or a neutral expression. Neuropsychological performance and symptoms ratings were recorded at baseline, immediately before scanning (1 hr), immediately after scanning (2 hr), and one hour post scanning (3 hr).

CBD had no significant effect on the gender discrimination task. Reaction times were significantly faster when processing 100% fearful faces than compared to 50% fearful and neutral faces. CBD had a significant effect on brain activation in response to faces with emotional expressions, decreasing activation in the right posterior cingulate gyrus and in the right cerebellum, when compared to placebo. Furthermore, a significant interaction effect was observed. In the right cingulate gyrus CBD attenuated activation during the processing of intense fearful faces but had no effect of neural response to neutral or mild fearful faces.

CBD significantly modulates the neurophysiological response associated with anxiety.

This study examined the effect of Delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD) on brain activation during a motor inhibition task.

Functional magnetic resonance imaging and behavioural measures were recorded while 15 healthy volunteers performed a Go/No-Go task following administration of either THC or CBD or placebo in a double-blind, pseudo-randomized, placebo-controlled repeated measures within-subject design.

Relative to placebo, THC attenuated activation in the right inferior frontal and the anterior cingulate gyrus. In contrast, CBD deactivated the left temporal cortex and insula. These effects were not related to changes in anxiety, intoxication, sedation, and psychotic symptoms.

These data suggest that THC attenuates the engagement of brain regions that mediate response inhibition. CBD modulated function in regions not usually implicated in response inhibition.

The increased prevalence of metabolic syndrome in people with severe mental illness (SMI) is well documented. The International Diabetes Federation (IDF) criteria for metabolic syndrome are three or more of the following: waist circumference ( 80 cm (females), (94 cm (males) OR BMI (30, triglycerides >1.7 mmol/l or on treatment, raised blood pressure (systolic >130 mg Hg or diastolic >85 mm Hg, OR on treatment for hypertension), raised fasting blood glucose (.5.6 mmol/l) OR diagnosed type II diabetes) and reduced HDL cholesterol (< 1.03 mmol/l) OR on treatment.

The IMPACT RCT is a Department of Health funded trial of a health promotion intervention (HPI) delivered by care co-ordinators to people with SMI across South London, Kent and Sussex. The intervention is focussed on improving health by addressing modifiable lifestyle factors such as diet, physical activity, obesity, cigarette smoking, alcohol and substance use.

We investigated the prevalence of metabolic syndrome in a sample of 212 patients for whom we had relevant baseline measures.

Data (weight, BMI, waist circumference, blood pressure, fasting HDL cholesterol, triglycerides and glucose levels) were analysed on 212 patients.

45% of the sample met IDF criteria for metabolic syndrome. Mean BMI was 30.6, glucose 6.4 mmol/L, triglycerides 2.0 mmol/L, HDL 1.2 (mmol/L), waist circumference 105.8 cm, and BP 122/82 mm Hg.

Metabolic syndrome was highly prevalent in this sample, significantly increasing the risk of physical morbidity and potentially lowering life expectancy. There is an unmet need for health promotion interventions in order to lower morbidity and mortality risk in these populations.

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.

In recent years the association between sexual dysfunction (SD) and obesity in the general population has drawn major attention. Although sexual dysfunction is common in psychosis, its relationship with weight gain and obesity remains unclear.

To investigate the association between sexual dysfunction and obesity in a cohort of patients with first episode psychosis.

Sexual function was assessed in a cohort of patients with first episode psychosis using the Sexual Function Questionnaire (SFQ). Anthropometric measures, including weight, BMI, waist, waist–hip ratio were investigated. Additionally, leptin and testosterone were investigated in male patients.

A total of 116 patients (61 males and 55 females) were included. Of these 59% of males and 67.3% of females showed sexual dysfunction (SD) according to the SFQ. In males, higher SFQ scores were significantly correlated with higher BMI (Std. β = 0.36, P = 0.01), higher leptin levels (Std. β = 0.34, P = 0.02), higher waist–hip ratio (Std. β = 0.32, P = 0.04) and lower testosterone levels (Std. β = −0.44, P = 0.002). In contrast, in females, SFQ scores were not associated with any of these factors.

While sexual dysfunction is present in both female and male patients with their first episode of psychosis, only in males is sexual dysfunction associated with increased BMI and waist–hip ratio. The association between SD, BMI, low levels of testosterone and high levels of leptin suggest that policies that lead to healthier diets and more active lifestyles can be beneficial at least, to male patients.

The aims of the study were to determine the prevalence of cardiometabolic risk factors and establish the proportion of people with psychosis meeting criteria for the metabolic syndrome (MetS). The study also aimed to identify the key lifestyle behaviours associated with increased risk of the MetS and to investigate whether the MetS is associated with illness severity and degree of functional impairment.

Baseline data were collected as part of a large randomized controlled trial (IMPaCT RCT). The study took place within community mental health teams in five Mental Health NHS Trusts in urban and rural locations across England. A total of 450 randomly selected out-patients, aged 18–65 years, with an established psychotic illness were recruited. We ascertained the prevalence rates of cardiometabolic risk factors, illness severity and functional impairment and calculated rates of the MetS, using International Diabetes Federation (IDF) and National Cholesterol Education Program Third Adult Treatment Panel criteria.

High rates of cardiometabolic risk factors were found. Nearly all women and most men had waist circumference exceeding the IDF threshold for central obesity. Half the sample was obese (body mass index ≥ 30 kg/m2) and a fifth met the criteria for type 2 diabetes mellitus. Females were more likely to be obese than males (61% v. 42%, p < 0.001). Of the 308 patients with complete laboratory measures, 57% (n = 175) met the IDF criteria for the MetS.

In the UK, the prevalence of cardiometabolic risk factors in individuals with psychotic illnesses is much higher than that observed in national general population studies as well as in most international studies of patients with psychosis.

What determines inter-individual variability to impairments in behavioural control that may underlie road-traffic accidents, and impulsive and violent behaviours occurring under the influence of cannabis, the most widely used illicit drug worldwide?

Employing a double-blind, repeated-measures design, we investigated the genetic and neural basis of variable sensitivity to cannabis-induced behavioural dyscontrol in healthy occasional cannabis users. Acute oral challenge with placebo or Δ9-tetrahydrocannabinol (THC), the main psychoactive ingredient in cannabis, was combined with functional magnetic resonance imaging, while participants performed a response inhibition task that involved inhibiting a pre-potent motor response. They were genotyped for rs1130233 single nucleotide polymorphisms (SNPs) of the protein kinase B (AKT1) gene.

Errors of inhibition were significantly (p = 0.008) increased following administration of THC in carriers of the A allele, but not in G allele homozygotes of the AKT1 rs1130233 SNP. The A allele carriers also displayed attenuation of left inferior frontal response with THC evident in the sample as a whole, while there was a modest enhancement of inferior frontal activation in the G homozygotes. There was a direct relationship (r = − 0.327, p = 0.045) between the behavioural effect of THC and its physiological effect in the inferior frontal gyrus, where AKT1 genotype modulated the effect of THC.

These results require independent replication and show that differing vulnerability to acute psychomotor impairments induced by cannabis depends on variation in a gene that influences dopamine function, and is mediated through modulation of the effect of cannabis on the inferior frontal cortex, that is rich in dopaminergic innervation and critical for psychomotor control.

Cannabis can induce transient psychotic symptoms, but not all users experience these adverse effects. We compared the neural response to Δ9-tetrahydrocannabinol (THC) in healthy volunteers in whom the drug did or did not induce acute psychotic symptoms.

In a double-blind, placebo-controlled, pseudorandomized design, 21 healthy men with minimal experience of cannabis were given either 10 mg THC or placebo, orally. Behavioural and functional magnetic resonance imaging measures were then recorded whilst they performed a go/no-go task.

The sample was subdivided on the basis of the Positive and Negative Syndrome Scale positive score following administration of THC into transiently psychotic (TP; n = 11) and non-psychotic (NP; n = 10) groups. During the THC condition, TP subjects made more frequent inhibition errors than the NP group and showed differential activation relative to the NP group in the left parahippocampal gyrus, the left and right middle temporal gyri and in the right cerebellum. In these regions, THC had opposite effects on activation relative to placebo in the two groups. The TP group also showed less activation than the NP group in the right middle temporal gyrus and cerebellum, independent of the effects of THC.

In this first demonstration of inter-subject variability in sensitivity to the psychotogenic effects of THC, we found that the presence of acute psychotic symptoms was associated with a differential effect of THC on activation in the ventral and medial temporal cortex and cerebellum, suggesting that these regions mediate the effects of the drug on psychotic symptoms.

We conducted a systematic review to assess the evidence for specific effects of cannabis on brain structure and function. The review focuses on the cognitive changes associated with acute and chronic use of the drug.

We reviewed literature reporting neuroimaging studies of chronic or acute cannabis use published up until January 2009. The search was conducted using Medline, EMBASE, LILACS and PsycLIT indexing services using the following key words: cannabis, marijuana, delta-9-tetrahydrocannabinol, THC, cannabidiol, CBD, neuroimaging, brain imaging, computerized tomography, CT, magnetic resonance, MRI, single photon emission tomography, SPECT, functional magnetic resonance, fMRI, positron emission tomography, PET, diffusion tensor MRI, DTI-MRI, MRS and spectroscopy.

Sixty-six studies were identified, of which 41 met the inclusion criteria. Thirty-three were functional (SPECT/PET/fMRI) and eight structural (volumetric/DTI) imaging studies. The high degree of heterogeneity across studies precluded a meta-analysis. The functional studies suggest that resting global and prefrontal blood flow are lower in cannabis users than in controls. The results from the activation studies using a cognitive task are inconsistent because of the heterogeneity of the methods used. Studies of acute administration of THC or marijuana report increased resting activity and activation of the frontal and anterior cingulate cortex during cognitive tasks. Only three of the structural imaging studies found differences between users and controls.

Functional neuroimaging studies suggest a modulation of global and prefrontal metabolism both during the resting state and after the administration of THC/marijuana cigarettes. Minimal evidence of major effects of cannabis on brain structure has been reported.