Cannabis and Cocaine Reduced Impulse Control and Brain Connectivity, But Only in People With Certain Genetics
Both cannabis and cocaine increased impulsivity and reduced brain reward circuit connectivity, but only in drug users with a genetic variant that predisposes to higher dopamine levels.
Quick Facts
What This Study Found
Researchers gave 122 regular drug users acute doses of cannabis, cocaine, and placebo and measured cognitive impulsivity and brain connectivity. The effects of both drugs depended heavily on a specific genetic variant (DBH rs1611115) that controls how efficiently dopamine is converted to noradrenaline.
In participants with the low-activity variant (CT/TT genotype), both cannabis and cocaine increased cognitive impulsivity on a matching task and reduced functional connectivity between the nucleus accumbens (the brain's reward center) and multiple cortical regions. In participants with the high-activity variant (CC genotype), neither drug significantly affected impulsivity or connectivity.
The researchers propose that individuals with low-activity DBH genotypes experience a drug-induced hyperdopaminergic state that disrupts impulse control circuits, while those with high-activity genotypes have enough enzyme activity to buffer the dopamine surge.
Key Numbers
122 drug users. Cannabis dose: 450 micrograms/kg THC. Cocaine dose: 300 mg. CT/TT genotype carriers showed increased impulsivity and reduced corticostriatal connectivity. CC genotype carriers showed no significant effects.
How They Did This
This was a controlled within-subject study. 122 regular drug users received acute doses of cannabis (450 micrograms/kg THC), cocaine (300 mg), and placebo across sessions. Cognitive impulsivity was measured with the Matching Familiar Figures Test. Resting state fMRI was performed in a subset to measure functional connectivity. Participants were genotyped for DBH rs1611115.
Why This Research Matters
This is one of the clearest demonstrations that genetics can determine whether a drug impairs cognitive function. The same dose of cannabis or cocaine had completely different effects depending on a single gene variant. This has implications for understanding why some people are more vulnerable to drug-related impairment and addiction.
The Bigger Picture
The idea that some people are genetically more vulnerable to drug effects is widely suspected but rarely demonstrated this clearly. By showing that a single genetic variant determines whether cannabis and cocaine impair impulse control, this study provides both a biological mechanism and a potential target for personalized treatment approaches.
What This Study Doesn't Tell Us
All participants were regular drug users, so results may not apply to occasional users or non-users. The study tested acute effects only; chronic effects may differ. The sample was genotyped after the study, so groups were not balanced by design. The fMRI subset was smaller than the full behavioral sample.
Questions This Raises
- ?Could DBH genotyping help identify individuals at higher risk for drug-related impairment?
- ?Would pharmacological approaches targeting dopamine-to-noradrenaline conversion reduce impulsivity in at-risk drug users?
- ?Do these genetic effects influence the transition from use to addiction?
Trust & Context
- Key Stat:
- Same doses of cannabis and cocaine impaired impulse control in one genotype group but not another.
- Evidence Grade:
- Moderate evidence from a controlled within-subject trial with a reasonable sample size, though the genetic analysis was post-hoc rather than prospectively designed.
- Study Age:
- Published in 2016. Pharmacogenomic approaches to substance use disorders remain an active research area.
- Original Title:
- Cannabis and cocaine decrease cognitive impulse control and functional corticostriatal connectivity in drug users with low activity DBH genotypes.
- Published In:
- Brain imaging and behavior, 10(4), 1254-1263 (2016)
- Authors:
- Ramaekers, J G(6), van Wel, J H, Spronk, D, Franke, B, Kenis, G, Toennes, S W, Kuypers, K P C, Theunissen, E L, Stiers, P, Verkes, R J
- Database ID:
- RTHC-01245
Evidence Hierarchy
Participants are randomly assigned to treatment or placebo groups to test cause and effect.
What do these levels mean? →Frequently Asked Questions
Do genetics determine how cannabis affects you?
This study found that a specific gene variant (DBH) determined whether cannabis increased impulsivity and disrupted brain connectivity. People with one version of the gene were significantly affected, while those with another version were not.
Could genetic testing predict who is more vulnerable to cannabis impairment?
This study suggests it might be possible. The DBH gene variant identified here affected responses to both cannabis and cocaine, potentially offering a biomarker for vulnerability. However, this would need much more research before any clinical application.
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Cite This Study
https://rethinkthc.com/research/RTHC-01245APA
Ramaekers, J G; van Wel, J H; Spronk, D; Franke, B; Kenis, G; Toennes, S W; Kuypers, K P C; Theunissen, E L; Stiers, P; Verkes, R J. (2016). Cannabis and cocaine decrease cognitive impulse control and functional corticostriatal connectivity in drug users with low activity DBH genotypes.. Brain imaging and behavior, 10(4), 1254-1263.
MLA
Ramaekers, J G, et al. "Cannabis and cocaine decrease cognitive impulse control and functional corticostriatal connectivity in drug users with low activity DBH genotypes.." Brain imaging and behavior, 2016.
RethinkTHC
RethinkTHC Research Database. "Cannabis and cocaine decrease cognitive impulse control and ..." RTHC-01245. Retrieved from https://rethinkthc.com/research/ramaekers-2016-cannabis-and-cocaine-decrease
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkTHC research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.