What the top US cop who writes a column as 'The Drug Warrior' thinks the legalisation of medical marijuana might mean for us in NZ.

OPINION: In 1996, California was the first state in the US to legalise cannabis for medicinal purposes. As New Zealand debates whether they will do the same, I ask that New Zealanders look at the history of legalisation/decriminalisation in the United States. There has been a large amount of propaganda from both sides of the debate, but somewhere in in the middle are the facts.

What we do know can be gleaned from a report from the High Intensity Drug Trafficking Area program, or HIDTA, a department that reports directly to the White House. HIDTA wrote a report in 2015 that looked at the impacts of marijuana legalisation in Colorado after that state legalised Cannabis in 2013.

In 2014, when marijuana businesses began operating, there was a 32 per cent increase in marijuana related traffic deaths in just one year (2013-2014). Colorado marijuana related traffic deaths increased 92 per cent from 2010 - 2014.

SUPPLIED Keith Graves is a top US detective with views on cannabis law reform and what it might mean for New Zealand.

Drug related expulsions from schools increased 40 per cent from school years 2008/2009 to 2013/2014. The vast majority for marijuana violations. Positive THC urinalysis tests for juvenile probationers increased 20 per cent since marijuana was legalised in 2013.

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In 2014, there was a 29 per cent increase in the number of marijuana related emergency room visits in only one year. There was also a 225 per cent increase in marijuana related exposures to children in Colorado after commercialisation of marijuana (2006-2008 to present).

On a personal note, I remember vividly when California made its move to decriminalisation of medical marijuana. At the time, I was a Narcotics Detective tasked with investigating major drug crimes. Also, my mother had just died from cancer, so I paid close attention to the legalisation debate. I was truly on the fence since I had interests in both sides of the debate.

There are currently medications made from synthetic THC. These medications (Sativax and Marinol) are made in a laboratory and have none of the ill effects of marijuana. It is truly medicine. My mother used Marinol while she was sick and it did help immensely.

There are no controls on marijuana. It will be diverted more for recreational use than to help truly sick people. Additionally, a recent study in California found that the average medical marijuana patient in that state was a young male with a history of drug abuse with no known medical problems.

History is a predictor of the future. We know from our history that decriminalisation will increase driving under the influence (DUI) deaths, increase youth drug use and will increase accidental exposures to our most innocent citizens; children.

If you keep possession of marijuana a crime, you are not hurting sick people. There are synthetic THC medicines available without the negative side effects of marijuana. What you will do is create a whole new problem of traffic deaths, accidental exposures and increased drug use among our youth.

Keith Graves has taught in more than 300 police agencies and over 100,000 personnel throughout the US, as well as military, federal agencies and foreign entities about drug use and drug trends. He has been a police officer in the San Francisco Bay area since 1990 and is currently a supervisor for the Special Operations Unit dedicated to narcotic, vice and gang investigations.

He is one of the world's foremost experts on drug trends, is an advisor to governments and regularly presents his training programmes to audiences around the world.