U.S. scientists found marijuana regulates both anxiety and the body’s fight-or-flight response. They say their findings lend credence to the claims of some users of the drug who believe it reduces their anxiety levels.
However, this contradicts previous research which has linked the drug to anxiety, depression, schizophrenia and bipolar disorders.
Researchers at Vanderbilt University, in Tennessee, discovered there are receptors through which marijuana can exert its effects in a key emotional hub in the brain.
They say these cannabinoid receptors can be identified in the amygdala in mice.
The amygdala is the part of the brain that is involved in regulating anxiety and the fight-or-flight response.
The study, which was led by Dr Sachin Patel and published in the journal Neuron, also showed for the first time how nerve cells in this part of the brain make and release their own natural ‘endocannabinoids’.
The natural endocannabinoid system regulates anxiety and the response to stress by dampening signals in the brain.
It was previously known that when a person is exposed to chronic stress, or severe emotional trauma, there can be a reduction in the production of natural endocannabinoids.
When this happens, anxiety levels tend to increase.
Smoking marijuana can reduce this anxiety because the effect of its cannabinoids on the cannabinoid receptors makes up for the reduction in the production of natural endocannabinoids.
However, chronic use of the drug can, paradoxically, increase anxiety as the drug reduces the efficiency of the brains’ cannabinoid receptors.
This can trigger a vicious cycle that can leave people addicted to the drug.
Dr Patel said the study ‘could be highly important for understanding how cannabis exerts its behavioural effects’.
He added: ‘We know where the receptors are, we know their function, we know how these neurons make their own cannabinoids.
‘Now can we see how that system is affected by … stress and chronic [marijuana] use. It might fundamentally change our understanding of cellular communication in the amygdala.’