A permissive inference is not a mandatory presumption; a permissive inference solely means that the fact of there being five nanograms or more of THC may be a basis to infer intoxication, but it is not required that intoxication be inferred from that fact. The defense can still present evidence to contradict that presumption and potentially convince the jury that despite there being more than five nanograms, the defendant actually was not intoxicated. A habitual smoker of marijuana, for example, is going to consistently have a high level of THC in his blood even if he has not smoked recently.

However, the law is the clear that if the driver did possess a valid medical marijuana license at the time of the offense, the prosecution cannot use that against the driver in their case in chief. Similarly, the fact that a driver has a medical marijuana card on him does not give a police officer probable cause to request that the driver submit to the blood test.

In any prosecution for driving under the influence of marijuana, your defense attorney likely will have an independent retest of the blood sample done to take another look, or perhaps a more detailed look, at those THC levels. There is a question of active versus inactive THC levels, particularly with frequent smokers – recent smoking activity is manifested in active levels, however, smoking activity over the last few weeks manifests in inactive levels. The tests performed by the state will not break down your results such that this distinction is analysed, and it will be up to the lab selected by your own attorney to do this. Privately performed tests are also more accurate than tests performed by the state.