Adverse Effects of Recreational and Medical Cannabis

Summary & key facts

This review looks at what we know about the harms and some benefits of marijuana when people use it for fun or for health. The authors say cannabis changes how brain chemicals work, so it can ease chronic pain and improve appetite or nausea for some people. But the overall evidence is low quality, and regular or early use is linked to worse memory, attention and thinking, brain changes on scans, and a risk of dependence in about 1 in 10 users. It is not clear how much of these effects go away after stopping or what the best treatments are for cannabis dependence.

Key facts:

• The paper reviewed harms and possible medical uses of marijuana for both recreational and medical users.
• Cannabis works by acting on the brain's cannabinoid system and changes the release of brain chemicals such as GABA, glutamate, dopamine, acetylcholine and norepinephrine.
• These chemical changes affect reward, learning and how pain is felt.
• Overall, the research available is mostly low quality, so conclusions about benefits and harms are still uncertain.
• Cannabis can relieve chronic pain for some people, and some users report about half or more pain relief compared with placebo in studies.
• Short-term memory is impaired while using cannabis, and long-term use is linked to bigger memory problems, slower thinking, worse attention and less effort on tasks.
• Brain scans in long-term users have shown smaller hippocampus size or lower density, and starting use at a younger age appears to raise the risk of lasting thinking problems.
• About 1 in 10 people who use cannabis meet criteria for lifetime dependence, though cannabis dependence seems different and often less common than dependence on some other drugs.
• It is still unclear whether stopping cannabis fully reverses addiction or cognitive changes, and there is not good data on how best to treat cannabis dependence.

Abstract

Purpose of Review: This comprehensive review discusses the adverse effects known today about marijuana, for either medical or recreational use. It reviews the role of cannabis in the treatment of chronic pain, cognitive and neurological adverse effects, special cases and addiction. Recent Findings: Cannabinoids work through the endocannabinoids system and inhibit the release of GABA and glutamate in the brain, impact neuromodulation, as well as dopamine, acetylcholine and norepinephrine release. They affect reward, learning and pain. The use of cannabis is increasing nationally and world-wide for both recreational and medicinal purposes, however, there is relatively only low quality evidence to the efficacy and adverse effects of this. Cannabis and its derivatives may be used for treatment of chronic pain. They are via CB1 receptors that are thought to modulate nociceptive signals in the brain. CB2 receptors in the DRG likely affect pain integration in the afferent pathways, and peripherally CB2 also affects noradrenergic pathways influencing pain. A large proportion of users may see more than 50% of chronic pain alleviation compared with placebo. Cannabis affects cognition, most notably executive function, memory and attention, and may deteriorate the boundary between emotional and executive processing. Cannabis impairs memory in the short run, which become more significant with chronic use, and may also be accompanied by poorer effort, slower processing and impacted attention. It is generally believed that long-term use and earlier age are risk factor for neurocognitive deficits; neuroimaging studies have shown reduced hippocampal volume and density. Executive functions and memory are worse in adolescent users versus adults. Cannabis addiction is different and likely less common than other addictive substances, but up to 10% of users meet criteria for lifetime cannabis dependence. Addiction patterns may be linked to genetic and epigenetic differences. It is still unclear whether abstinence reverses patterns of addiction, and more research is required into this topic. Summary: Cannabis use has become more abundant for both medical and recreational use. It carries likely benefits in the form of analgesia, anti-emesis and improved appetite in chronic patients. The evidence reviewing adverse effects of this use are still limited, however, exiting data points to a clear link with neurocognitive deterioration, backed by loss of brain volume and density. Addiction is likely complex and variable, and no good data exists to support treatment at this point. It is becoming clear that use in earlier ages carries a higher risk for long-term deficits. As with any other drug, these risks should be considered alongside benefits prior to a decision on cannabis use.

Topics

Cannabis and Cannabinoid Research Forensic Toxicology and Drug Analysis Psychedelics and Drug Studies

Categories

Health Sciences Medicine Pharmacology

Tags

Addiction Adverse effect Affect (linguistics) Cannabidiol Cannabis Chronic pain Cognition Communication Effects of cannabis Endocannabinoid system Functional neuroimaging Internal medicine Medicine Neurocognitive Neuroscience Pharmacology Psychiatry Psychology Receptor

Substances

Cannabis

Conditions & symptoms

Addiction Chronic Pain Addiction or harmful habbits Chronic pain