A new scientific research review titled “The Effects of delta-9-Tetrahydrocannabinol on the Dopamine System” reveals a complex relationship between tetrahydrocannabinol (THC) and dopamine. This review of human and animal studies highlights the need for deeper scientific understanding and increased awareness among consumers. While many cannabis consumers may use cannabis for mental health improvement, long-term cannabis use is associated with a weakening of the dopamine system.
Acute Cannabis Use on Dopamine: Does THC Increase Dopamine?
Acute THC use causes increased dopamine release and increased neuron activity [1]. However, long-term effects and effects on the developing brain can negatively impact dopaminergic activity. Dopaminergic activity is the activity of dopamine neurotransmitters. While we mostly associate dopamine with mental health, it is important to note that dopaminergic drugs are also used for treating Parkinson’s disease and endocrine disorders.
- THC affects the body via the endocannabinoid system
- The psychoactive effects of THC are exerted through cannabinoid receptor 1 (CB1)
- Psychoactive and rewarding effects of THC are mediated by the dopaminergic system
Dopaminergic neurons are modulated by the endocannabinoid system [1]. Endocannabinoids that are naturally produced by the body modulate dopamine transmission. Since cannabinoids from cannabis are analogous to endocannabinoids, they can exert similar actions. However, since cannabinoids from cannabis are not native to the body, they alter the activity of the endocannabinoid system by supplementing natural cannabinoid levels.
Acute THC Use and Dopamine: Effect of THC on Dopamine Levels in the Brain
Overall, human studies show THC increases activity in frontal and subcortical brain regions [1]. These are the regions where CB1 is most concentrated. Human studies have also observed increased dopamine release following THC consumption. However, there have also been observations of reduced dopaminergic processing in humans following THC use. Researchers have also noted correlations between THC dose and dopamine in animal models:
- Low doses of THC can increase dopamine synthesis
- High doses of THC can reduce dopamine synthesis
- THC may also alter dopamine metabolism in a dose-dependant manner
- THC may increase the firing rates of dopamine neurons
Chronic THC Use and Dopamine in Humans
Molecular imaging studies of chronic cannabis users have revealed decreases in dopamine synthesis capacity [1]. Studies have also observed that chronic cannabis users do not release as much dopamine when stimulated. The severity of reduced dopamine release was proportional to the severity of chronic cannabis use. That research study also noted negative impacts on cognition and working memory. While stimulation-induced dopamine responses were blunted, chronic cannabis users did not have altered dopamine responses in terms of stress-induced dopamine response which involved different parts of the brain. Researchers have also found that chronic cannabis users have a reduced density of dopamine transporters that is proportional to the severity of use.
Dopamine in Ex-Cannabis Users and Adolescence
Interestingly, abstinent and ex-cannabis users appear to have dopamine receptor systems that function normally [1]. However, the overall abundance of dopamine receptors is reduced in people who started using cannabis at younger ages. Adolescence is a key time for brain development, and cannabinoid use in teens has consequences in adulthood. Exposure to THC in adolescence can lead to changes in dopamine receptor gene expression and reductions in transmitters in adulthood. Likewise, adults who used cannabis in adolescence also have reduced dopaminergic responses to stimulus and stress. The acute increases in neuron firing seen in acute cannabis use are also not seen in adults with adolescent cannabis use.
Risks of Chronic Cannabis Use
The relationship between THC and dopamine is very important because it is likely the link to many of the adverse effects of chronic cannabis use. Cognitive impairment, working memory impairment, lack of motivation, and negative emotional and mood impacts are all risks of chronic cannabis use with links to dopaminergic function [1]. It is important for cannabis users to understand that while THC can have many benefits, it can also backfire when use becomes chronic.
Final Thoughts on THC and Dopamine
While this robust research review provides amazing insights into how cannabis affects dopamine systems, it also highlights the need for more research to bridge gaps between human and animal studies and explore inconsistencies among research. This paper also points out the importance of preventing adolescent cannabis use and encouraging moderation in adult cannabis users. Researchers are also seeking a better understanding of the point where THC’s effects on dopamine function become irreversible.
References
- Bloomfield, M. A., Ashok, A. H., Volkow, N. D., & Howes, O. D. (2016). The effects of Δ9-tetrahydrocannabinol on the dopamine system. Nature, 539(7629), 369-377.
