Law enforcement is still looking for a a way to properly test for impairment in drivers when it comes to consuming marijuana. As Oklahoma's medical marijuana program begins regulating they want patients to know that even with a state registered medical marijuana ID card they can be charged with a DUI. Like alcohol testing, there is a way to test the amount of THC in a person's body, however the problem comes from the fact that cannabis is stored in a person's fat cells and therefore stays in the body long after any impairment is gone. It is difficult for law enforcement to be able to tell if a driver is impaired purely from a blood test because a frequent cannabis user will have a higher amount of THC in their system while not being as impaired as a less frequent user with less THC who might actually be impaired.
"When you consume marijuana it actually goes to the fatty parts of your body and therefore it can stay in your system longer. you can't say whether or not when they consumed it, if it was from recent use or past use."
Grafton said even if have a medical marijuana license, you can still be charged with a DUI.