Written by: Dr Low Tchern Kuang Lambert, Honorary Treasurer, on behalf of Singapore Psychiatric Association
Edited by: Dr Wong Kim Eng, Emeritus Consultant
Cannabis, also known as Weed, Marijuana or Ganja belongs to the Cannabinoid class of drugs. The principal psychoactive compound being tetrahydrocannabinol or THC for short. It is usually rolled up into a joint and smoked. However it can also be eaten in the form of cakes or candies as in “pot brownies” or “Marijuana Munchies” respectively or brewed as a tea. When smoked as a joint, there are characteristic odours which can be easily identified. The acute effects of the drug include euphoria and a relaxed feeling (“stoned” in layman parlance) but it can also induce distressing hallucinations and feelings of paranoia.
Whilst legalized in some states in the USA, Cannabis is a class A drug in Singapore which means there are severe penalties associated with its use. Like other Class A drugs, e.g. Heroin, Methamphetamine, this means that any physician who knows of or suspects that a patient is using Marijuana has a legal obligation to notify the Central Narcotics Bureau within 7 days as per the Misuse of Drug Regulations, Section 19. The website for notification is www.cnb.gov.sg and users can log in using their SINGPASS account. When in doubt, a urine drug screen can be useful as Cannabis can be detected for several weeks after its last use in chronic users.
In 2013, based on the Central Narcotics Bureau drug situation report, Cannabis was the third most commonly abused drug.1 This is as compared with the United States where according to the Drug Enforcement Administration (DEA) website, it was stated that Cannabis was the most widely available and commonly abused illicit drug in the USA in 2013.2 DSM-V has also stated that Cannabis is probably the world’s most commonly used illicit substance.3 Cannabis use has been associated with several long term negative effects. There is a well known association between psychoses and cannabis use.4-7 Cannabis has also been linked to the development of schizophrenia when taken over a long period off time.4 Several reports have also indicated adverse effects of Cannabis on a variety of cognitive domains such as working memory and executive function.8-10
Some experts postulate the Cannabis use serves as a “gateway” drug, serving as an entry level drug towards more severe addictions like Heroin and Methamphetamine addictions although this “gateway” pattern observed may well be due to unmeasured background common factors rather than a true effect of specific drugs on the subsequent use of other drugs.11
An article published in BMJ revealed that the purity of Cannabis increased by 161% between 1990 and 2007.12 Whilst previously thought not to induce physical dependence but only psychological dependence, the increasing purity of Cannabis seen in the market has resulted in DSM-V acknowledging the presence of a physical symptoms secondary to Cannabis withdrawal.3 Such withdrawal symptoms can include irritability, feelings of restlessness, insomnia, anxiety or restlessness.3 The higher the purity of Cannabis, the more likely the risk of physical dependence and withdrawal symptoms. For a diagnosis of Cannabis Use Disorder under DSM-V, the patient would have to display typical symptoms over a 12 month period with clinically significant distress or impairment. These symptoms include saliency, cravings, tolerance, withdrawal symptoms, unsuccessful attempts to cut down, use in hazardous situations and continued use despite adverse consequences.3
More information on Cannabis can be found as a factsheet on the DEA website.13
- APA: Diagnostic and Statistical Manual. 5th edition. Arlington: American Psychiatric Association; 2013.
- Manrique-Garcia E, Zammit S, Dalman C, Hemmingsson T, Andreasson S, Allebeck P. Cannabis, schizophrenia and other non-affective psychoses: 35 years of follow-up of a population-based cohort. Psychol Med 2012;42:1321-8.
- Drake RE, Wallach MA, Hoffman JS. Housing instability and homelessness among aftercare patients of an urban state hospital. Hosp Community Psychiatry. 1989;40:46-51.
- Dixon L. Dual diagnosis of substance abuse in schizophrenia: prevalence and impact on outcomes. Schizophr Res 1999;35 Suppl:S93-100.
- Negrete JC. Clinical aspects of substance abuse in persons with schizophrenia.Can J Psychiatry. 2003;48:14-21.
- Thames AD, Arbid N, Sayegh P. Cannabis use and neurocognitive functioning in a non-clinical sample of users. Addict Behav 2014;39:994-9.
- Becker MP, Collins PF, Luciana M. Neurocognition in college-aged daily marijuana users. J Clin Exp Neuropsychol 2014;36:379-98.
- Lisdahl KM, Wright NE, Kirchner-Medina C, Maple KE, Shollenbarger S. Considering Cannabis: The Effects of Regular Cannabis Use on Neurocognition in Adolescents and Young Adults. Curr Addict Rep 2014;1:144-156.
- Degenhardt L et al. Evaluating the drug use “gateway” theory using cross-national data: consistency and associations of the order of initiation of drug use among participants in the WHO World Mental Health Surveys. Drug Alcohol Depend. 2010;108:84-97.
- Werb D, Kerr T, Nosyk B, Strathdee S, Montaner J, Wood E. The temporal relationship between drug supply indicators: an audit of international government surveillance systems. BMJ Open 2013;3:e003077