Teenage cannabis use may increases a person's risk of suffering from bipolar disorder in later life, new research suggests.
People who used cannabis at least two-to-three times a week at 17 years old are more likely to experience hypomania in their earlier 20s, according to the first study of its kind.
Hypomania is defined as an elevated mood alongside irritability or an inflated ego, an unrealistic sense of superiority, frenzied speech and a reduced need for sleep.
Such symptoms frequently occur in bipolar-disorder sufferers.
Lead author Dr Steven Marwaha from Warwick Medical School, said: 'Adolescent cannabis use may be an independent risk factor for future hypomania, and the nature of the association suggests a potential causal link.'
Cannabis is the most commonly-used drug in the UK, with 6.5 per cent of people aged between 16 and 59 taking it in the past year, which makes up around 2.1 million individuals.
Teenage cannabis use may increases a person's later risk of suffering from bipolar disorder
The zombie-drug 'spice' makes users significantly slower and unable to focus within just one hour, the first study of its kind reported last month.
Even at considerably lower doses than those taken recreationally, the controversial 'fake cannabis' and former 'legal high' makes people feel intoxicated within just 60 minutes and tired 12 hours later, the research adds, which is the first to investigate the drug's behavioural effects in humans.
Although the study's safety results were strong, with only fatigue and headache being reported, experts warn the dose used was exceptionally low.
Ian Hamilton, a cannabis researcher at York