Most of the studies assessing Cannabis Use Disorder (CUD) and neurocognitive functions are cross-sectional without examining the longitudinal changes in neurocognitive function at a within-subject level with respect to the continuum of cannabis use behavior, or mainly studying on the acute cannabis effect. As for the Genome-wide Association studies, the population analyzed for addressing the underlying genetic susceptibility between neurocognitive functions and/or cannabis use or CUD were almost exclusively based on African- or European- American samples or other Caucasian subjects, and thus generalizability to Chinese or to the non-Caucasian population definitely demands more studies.

With the upsweeping statistical figures of cannabis use in Hong Kong and Asia, and the substantial falls in the perceived risk and personal disapproval from using cannabis amongst young abusers, coinciding the global advocacy of de-criminalizing cannabis and the increased availability of recreational cannabis worldwide, it is reasonable to predict that there will be a further upsurge in numbers of all aged cannabis users in Hong Kong as in the other part of the world. Therefore, the SToP-C-PeCoG study proposed here as a prospective study in assessing the longer term changes in neurocognitive functions and the associated genetic risks for those repeated and active cannabis users without psychiatric co-morbidity is definitely warranted. The PeCoG study will not only provide the scientific evidence to further unveil the harmful effects on neurocognitive functions for those self-perceived "healthy" users, but also help to raise the public awareness and to improve the understandings to the long-term detrimental effects of cannabis amongst users and non-users. Furthermore, it will provide a chance to study the associated genetic risks for cannabis abusers, in particular in the Asian minority and Chinese, on CUD and poorer neurocognitive outcomes, with genetic vulnerability being generalizable to the local population in Asia.

The current study hypothesises that cannabis abusers have neurocognitive function decline over time, and genetic vulnerability is associated with cannabis abusers who have poorer neurocognitive outcomes or with the severity of CUD.

Inclusion Criteria:

• Age: 16 - 60 years old at the time of enrolment
• Able to read and communicate in English and/or Chinese
• Able to give informed consent
• Using cannabis or marijuana as the primary psychoactive substance of abuse
• Repeated and Active cannabis users as defined by Structured Clinical Interview for DSM-5 Disorders

Exclusion Criteria:

• Age <16 years old
• Unable to read English or Chinese
• Unable to give informed consent
• Had been diagnosed with other Substance Related Disorders, except for Tobacco Use Disorders due to the known frequent comorbid use for cannabis users (12)
• Currently taking regular prescribed psychiatric medications, including antipsychotics, antidepressants, mood stabilizers, anti-epileptics, benzodiazepines, hypnotics, and anti-cholinergic medications.
• Had been diagnosed with DSM-5 disorders, other than Cannabis Use and related disorders

16-60 years old cannabis users

data without identifiable