In my opinion, the answer to your question is yes. You can have an expert testify that a medical marijuana user may test positive several days after ingesting marijuana. An expert can also testify that a driver is likely not impaired at 2ng active THC. There are many scientific studies that support such testimony and the state's expert may also be aware of these facts. This could result in the jury finding the defendant not guilty. However, as I understand AZ law, even the presence of the metabolite can be used as evidence of impairment (even though it is not). If you are charged with DUID in AZ you should immediately contact a skilled DUID attorney who understands the science behind marijuana metabolism in order to build an effective defense. If you want more information on this, I recently published a chapter on this subject in "Utilizing Forensic Evidence in Criminal Cases" 2014 ed. You can find the book on Amazon.
This probably belongs on the criminal law/ DUI side of AVVO. But that said, there are clearly contradictions and issues to be worked out for medical marijuana users. It the legislature doesn't clean this up (and they likely won't) the courts will have to attempt to reconcile the obvious discrepancies.
I have addressed these concerns in a recent article to be published in the next issue of Attorney at Law magazine distributed in Arizona/Maricopa County. I have summarized the article in a legal guide on AVVO. I hope it addresses your concerns.
DISCLAIMER THESE COMMENTS ARE NOT LEGAL ADVICE. The answer given above serves an educational purposes only and provides general information and a basic understanding of the applicable law. Answering this question does not create an attorney-client relationship or otherwise require further consultation this website is not intended to provide anyone specific legal advice for their specific issue. Actual legal advice can only be provided after consultation by an attorney licensed in your jurisdiction. Anyone using the site expressly consents that there is no attorney client privilege between any person and any attorney responding. The answer provided does not substitute for any professional and competent legal advice by a licensed professional attorney in the applicable jurisdiction who has reviewed all discovery and an opportunity to discuss the issues specific to the case with the client. The attorney above attempted to provide competent professional information, however, the law and its applications change frequently and may vary greatly from other U.S. jurisdictions and locales.Therefore, any information and materials provided above are general in nature, and may not apply to specific factual specific legal circumstances involving one’s personal legal issues. Contact an experienced criminal defense lawyer admitted to practice in your State under an attorney-client privilege to further receive a competent legal advice before making any important decisions about your particular legal issue.
Unfortunately, as the law stands now, having a card is "not" a defense to either an A1 or A3 charge. Cases are making their way up on appeal and the matter will eventually be resolved in the appellate courts or by the Legislature.