Adverse Effects of Recreational and Medical Cannabis

Summary & key facts

This review looked at what we know about harmful and helpful effects of marijuana when people use it medically or for fun. Researchers say cannabis can reduce chronic pain, nausea, and increase appetite for some patients. But it also changes how the brain works, can harm memory and attention—especially if people start young or use it for a long time—and can lead to dependence in a minority of users. The overall quality of the evidence is still limited, so many findings are uncertain and more research is needed.

Key facts:

• Cannabis chemicals change how brain cells talk to each other and affect brain chemicals that control reward, learning, attention, and pain.
• Some studies report that many people with long-term pain get about half the pain relief from cannabis compared with placebo, but the overall evidence is low quality.
• Short-term cannabis use impairs memory, and long-term or early use is linked with worse thinking skills, slower processing, and poorer attention.
• Brain scans in studies have found smaller size or lower density in the hippocampus, a key memory area, in long-term users.
• About 10% of users meet criteria for lifetime cannabis dependence, though addiction seems less common than with some other drugs and likely depends on genetics and other factors.
• It is not clear yet whether stopping cannabis fully reverses addiction or long-term thinking problems; researchers say more studies are needed.
• For some chronic patients cannabis offers likely benefits like pain relief, reduced nausea, and increased appetite, but those benefits should be weighed against the possible brain and addiction risks.

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 medical cannabis

Conditions & symptoms

Addiction Chronic Pain Addiction or harmful habbits Chronic pain Difficulty focusing