At present there appears that the main studies being carried out are in the form of animal trials or pre-clinical/case studies on children with severe/recurrent epilepsy.
The Epilepsy Foundation has information on medical marijuana and epilepsy at http://www.epilepsy.com/learn/treating-seizures-and-epilepsy/other-treatment-approaches/medical-marijuana-and-epilepsy
Also a Medscape article at http://www.medscape.com/viewarticle/825642