In 1996, California became the first U.S. state to legalize medical cannabis with the passage of a public referendum, Proposition 215. For those who wanted legal access to cannabis for the treatment of medical conditions, Proposition 215 – and the identification system created six years later -- were successes. Physicians prescribing cannabis to patients and patients using it no longer had to fear criminal prosecution. However, this doesn’t mean there haven’t been any problems.

As described in an opinion piece by one of the drafters of Proposition 215, the law has failed to achieve its objective “to liberate patients from the expensive but questionable products from dubious sources.”1 Instead, a cannabis industry has been allowed to develop in the open marketplace with poor regulation and little or no quality control.

California had no requirements or regulations concerning the use of pesticides and fungicides by medical cannabis producers. The result? Testing in 2017 of 44 medical cannabis products for 16 pesticides found 41 (93 percent) contained pesticides at levels high enough that they would have been banned in other states.2

With the passing of Proposition 64 to legalization recreational use of cannabis, new challenges may rise. On the one hand, state regulators will implement a comprehensive new system to regulate production, including the use of pesticides, and sales. These regulations are expected to reduce the black market and make cannabis products safer.

On the other hand, prices may increase: those with a government-issued medical cannabis identification card won’t be required to pay a state sales tax but will be required to pay the mandatory 15 percent tax imposed by Proposition 64. Additional local taxes are also allowed under the recreational cannabis legislation.

Given the larger market for recreational cannabis, some commentators are concerned about its effects on the strains producers will cultivate. Much of the medicinal effect of cannabis is thought to be associated with cannabidiol (CBD), whereas recreational users want the highest level possible of delta-9-tetahydrocannabinol (THC), the compound that produces the “high.” As a result, there can be substantive differences in the chemical composition of strains created for medical and recreational use.

It has been estimated that by 2019, recreational cannabis spending will outpace medical cannabis sales. In Colorado there are already more cannabis dispensaries than Starbucks and McDonald’s locations combined.3 There is a danger production could shift to where the market is larger or more lucrative. As one medical cannabis user put it, “If it is legalized, more people who don’t respect it and just want to get high are going to take advantage of that. And people who genuinely need it as medicine will be misplaced and thrown to the side.”4

If, as anticipated, recreational cannabis is legalized in Canada in 2018, it may face some of the same challenges of California. Evidence for planning and decision-making will be required.

Author Details

The latest scientific evidence on this topic was reviewed by the Centre's leadership team. This evidence brief is written by Corinne Hodgson, DHealth, assessed for accuracy by Co-Director Dr. James MacKillop, PhD, an expert in addictions and mental health research. There are no conflicts of interest. Questions regarding this piece should be directed to Dr. James MacKillop (

  1. Medical marijuana in California: a history. A success, yes, but there are many unintended consequences. March 6, 2009.
  2. Grover J, Glasser M. Pesticides and Pot: What’s California Smoking? NBC Los Angles. February 23, 2017.
  3. Robinson M. The way people buy legal marijuana will change in 2019 – here’s what to expect. Business Insider. April 1, 2017.
  4. What happens to medical marijuana if recreational use becomes legal in California? The Mercury News. July 20, 2016.