Excessive cannabis use reduces dopamine levels according to new study

The researchers at Columbia University Medical Center, The New York-based researchers have discovered that heavy cannabis use has the same effect on the brain's dopamine system as chronic cocaine or heroin use: reduced dopamine levels in the brain can lead to attention and memory deficits.

Dopamine is a neurotransmitter that plays a key role in the brain's reward system, and is released in response to a pleasurable stimulus such as enjoying a dish, a romp or taking a drug. This is what makes many substances so addictive (including chocolate), although research suggests that excessive use of these substances causes a dopamine imbalance, with lower concentrations released in the brain.

Cannabis and dopamine

Dopamine deficiency is associated with reduced cognitive performance. Given that THC is known to stimulate dopaminergic neurons throughout the brain, study leader Anissa Abi-Dargham explains that «it's important to take a closer look at the potential addictive effects of cannabis on key brain regions».

To do this, she and her team used a technique called positron emission tomography (PET) to examine the levels of dopamine released in the striatum (a part of the brain) in 11 people addicted to cannabis after receiving an oral dose of amphetamine, which stimulates the brain to emit the neurotransmitter. The results, published in the journal Molecular Psychiatry, The results of a study carried out by the Institute of Medicine of the University of Geneva show that, compared with non-dependent subjects, the participants did indeed show reduced levels of dopamine.

To explore the impact of this discovery, the researchers then subjected the participants to tests designed to measure their cognitive functioning. Cannabis-dependent individuals scored worse for memory and attention than non-dependent individuals, leading the study authors to declare that «reduced dopamine levels may contribute to a negative functional impact on chronic cannabis users».

However, the researchers also point out that they were unable to «show a causal relationship» between cannabis use and dopamine deficiency, explaining that they cannot be entirely sure whether «dopamine deficiency is a pre-existing condition or the result of heavy cannabis use».

However, the main conclusion of the study is that the strong de cannabis use affects the long-term the dopaminergic system, and therefore the activities that depend on it.

Cannabis and schizophrenia

Taking their investigations a step further, the researchers also measured levels of another neurotransmitter called glutamate in the hippocampus, another brain region. In people with schizophrenia, high levels of glutamate in this part of the brain are known to adversely affect dopamine levels, resulting in certain psychopathological symptoms.

Given that a link between excessive consumption of cannabis and schizophrenia has already been suggested, The researchers hypothesized that the dopamine deficits experienced by regular users could be modulated by glutamate, thus confirming the link. However, no signs of glutamate imbalance were detected in the participants' hippocampi. No smoking link between weed and schizophrenia could therefore be found.