Background There is an increasing international interest in patient and public involvement (PPI) in research, yet relatively little robust evidence exists about its impact on health and social care research.

This is the first international systematic review to focus on the impact of PPI on the people involved in the process. The beneficial and challenging impacts reported highlight the importance of optimising the context and processes of involvement, so creating the potential for PPI to impact positively on the research itself.

Neurocognitive impairment persists in patients whose bipolar disorder is in remission. This may represent a trait abnormality and be a marker of underlying neurobiological dysfunction.

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Objective To compare the analgesic efficacy and side effects of the synthetic cannabinoid nabilone with those of the weak opioid dihydrocodeine for chronic neuropathic pain. Design Randomised, double blind, crossover trial of 14 weeks' duration comparing dihydrocodeine and nabilone. Setting Outpatient units of three hospitals in the United Kingdom. Participants 96 patients with chronic neuropathic pain, aged 23-84 years. Main outcome measures The primary outcome was difference between nabilone and dihydrocodeine in pain, as measured by the mean visual analogue score computed over the last 2 weeks of each treatment period. Secondary outcomes were changes in mood, quality of life, sleep, and psychometric function. Side effects were measured by a questionnaire. Intervention Patients received a maximum daily dose of 240 mg dihydrocodeine or 2 mg nabilone at the end of each escalating treatment period of 6 weeks. Treatment periods were separated by a 2 week washout period. Results Mean baseline visual analogue score was 69.6 mm (range 29.4-95.2) on a 0-100 mm scale. 73 patients were included in the available case analysis and 64 patients in the per protocol analysis. The mean score was 6.0 mm longer for nabilone than for dihydrocodeine (95% confidence interval 1.4 to 10.5) in the available case analysis and 5.6 mm (10.3 to 0.8) in the per protocol analysis. Side effects were more frequent with nabilone. Conclusion Dihydrocodeine provided better pain relief than the synthetic cannabinoid nabilone and had slightly fewer side effects, although no major adverse events occurred for either drug. Trial registration Current Controlled Trials ISRCTN15330757.

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Serotonin (5-HT, 5-hydroxytryptamine) may have an important role in the maintenance of normal neuropsychological functioning. The method of acute tryptophan depletion (ATD) provides a pharmacological challenge by which central 5-HT levels can be temporarily decreased and effects on learning, memory and mood examined. Twenty healthy male volunteers were recruited to take part in this within-subject, double-blind, crossover study. Neuropsychological function was evaluated 4-6 h after ingestion of a control or 52 g tryptophan (TRP) depleting amino-acid drink. ATD significantly lowered levels of plasma total and free TRP (p < 0.001), but this did not affect mood or performance on tests of verbal and visuo-spatial learning and memory, attention or executive function. These results contradict previous findings; however, the degree of disruption of central 5-HT levels resulting from the use of the 52 g amino-acid protocol may be an important factor in explaining the lack of effect. By utilizing more specific probes of individual 5-HT receptor subtypes, future studies can fully explore the role of 5-HT in neuropsychological functioning and may elucidate the factors determining vulnerability to the effects of serotonergic dysfunction.