alan shackelford is a harvard-trained physician.is also among a handful of doctors in colorado who give prescriptions for medical marijuana. from the moment charlotte entered his office, he knew she was in trouble. while he was just examining her, she had two seizures. >> she had failed everything. there were no more options for her. everything had been tried, except cannabis. >> here's how scientists think it might work. marijuana is made up of two ingredients, thc -- that's the psychoactive part that makes you high, and cbd, also called cannabidiol. they think it regulates electrivity to help quiet the activity in the brain that causes seizures. >> dr. julie holland is the editor of the pot book, a complete guide to cannabis. >> for a long time the work on cannabis and epilepsy was sort of inconclusive. maybe it works. maybe it doesn't. they couldn't quite figure it out. it's only when they really started separating thc from cbd that they saw definitively, yes, cbd seems to really stop seizures. >> so the figges needed to find som