This might be of interest.
"The combination of THC and other MIXED CANNABINOIDS contained within CANNABIS stimulates a short-term spiking of GABA, but is followed by a subsequent LOWERING OF OVERALL GABA LEVEL; and hence overtime can CAUSE or EXACERBATE ANXIETY.

"There is some interesting recent research (and a growing number of annecdotal user reports) however that has indicated that PURE CANNABIDIOL might possibly be an effective ANXIOLYTIC, whereas the THC and/or some of the other MIXED CANNABINOIDS may be the cause of the long-term reduction in overall GABA levels, which can be avoided by ensuring that only the PURE CANNABIDIOL is administered"

http://www.longecity.org/forum/topic/54028-treating-anxiety-safely-effectively/