Tailoring medication to the needs of the individual has always been something of a hit-and-miss affair when it comes to anxiety. The prescribing doctor has no way of predicting whether a patient will respond positively to the prescription they are about to write. Almost inevitably this leads to a series of repeat visits where the patient attempts to describe the effects of their medication and the doctor tries to modify their prescription or dosage accordingly.

A team of researchers have now focused their attention on mechanisms of the brain that may one day help doctors prescribe medication with a lot more certainty. Dr Luan Phan and colleagues, have recently reported some interesting findings in the Journal of Neuroscience, using a combination of brain scans and marijuana.

Marijuana contains the active ingredient delta-9-tetrahydrocannabinol (THC). THC is known to help reduce the brain's response to threats in a region of the brain known as the amygdala. The amygdala is an almond shaped, almond sized, area of the brain that helps to regulate emotions.

Sixteen recreational users of marijuana took part in a placebo controlled experiment in which some were given capsules containing THC and others were given identical capsules without THC. The volunteers were then shown a series of faces with different emotional expressions. The reaction of the brain to these expressions was recorded in real time using functional magnetic resonance imaging (fMRI).

The research team were able to determine areas of brain that responded to different emotions. They noted that THC reduced the brain's response to threatening images whilst leaving other areas of the brain unaffected. This pointed to THC as having a specific and direct effect on a region of the brain rich in a receptor known as CB1.

Although it is known that CB1 is part of the brain's natural cannabinoid system, little is known about the effects of THC on this system. The body's own cannabinoids are involved in anxiety so the fact that THC appears to suppress this activity could point the way for new generations of anti-anxiety drugs. A useful bi-product of the research could help in the understanding of addictive behaviors.

Research is ongoing and will next test the effects of Zoloft (sertraline), a selective serotonin inhibitor (SSRI) approved for use in cases of social anxiety and other anxiety disorders.