Yet with concern about contaminated legal cannabis rising in recent months with reports of recalls and new state laws that require testing of marijuana products, should the state adopt its own quality standards?
Will Humble, who served as Arizona Department of Health Services director from 2009 to 2015, said he doesn't think the state needs to enforce purity standards for medical marijuana sold at dispensaries, at least for now.
"Until I was to see survey data of illness and injury that was compelling, I would say where's the public health mandate to take action?" Humble said.
It's unclear how concerned the public and cannabis consumers should be, considering marijuana's generally excellent safety record. Recorded instances of dispensary cannabis sickening people because of contamination in Arizona or elsewhere don't seem to exist.
That's not to say it can't happen.
Recent articles about dispensary marijuana tainted by pesticides, herbicides, fungicides, heavy metals, or possible pathogens have raised awareness about the potential problem.
Last month, an edibles manufacturer pulled 1,000 products from the shelves in Colorado because of "potentially unsafe pesticide residue." In March, the state of Oregon ordered its first recall of marijuana flower that contained above-average levels of pesticides.
The Arizona Medical Marijuana Act, passed narrowly by voters in 2010, contains no provisions for mandatory testing or enforcement of any safety standard for cannabis.
State-licensed dispensaries and the Marijuana Policy Project wrote a testing standard into Prop 205, the November ballot measure that would have legalized marijuana for adults 21 and older, but voters rejected the measure. The defeat of Prop 205 ensured that any safety standards by Arizona medical-marijuana dispensaries would remain self-imposed.
Arizona isn't alone among states with dispensaries: Michigan, Montana, and Rhode Island don't have any testing standards either, a list published by Leafly.com in February shows. The latter two states, though, have relatively small patient counts of under 20,000 people each. Arizona has about 115,000 patients and Michigan has 182,000, recent statistics show. (UPDATE: Michigan, which has no state-sanctioned dispensaries, passed a new package of laws in December that calls for dispensary licenses to be issued — and requires the future dispensaries to test their products.)
Washington, D.C., doesn't require testing, but its recreational-marijuana law doesn't provide for sales of cannabis.
All other states with recreational or medical marijuana require testing, or even inspection, for contaminants. Some states require additional tests for cannabis compounds including THC and cannabidiol (CBD), or the moisture content of dried buds.
California, for example, is moving to create strict guidelines and standards for the testing of its legally sold cannabis based on the recreational marijuana law its voters approved in November. Nevada, Massachusetts, Maine, and other states with new cannabis laws are moving in that direction.
But not Arizona.
According to Humble, who's now the executive director for the nonprofit Arizona Public Health Association, current state ADHS Director Cara Christ could probably make mandatory testing part of the medical-marijuana program with a rule change.
The Arizona Legislature also could pass a law ordering the ADHS to mandate testing.
Humble said he's not sure it's necessary.
He could have tried to mandate testing when he was director, he admitted.
The 2010 law gives rule-making authority for the program to the DHS that would allow the agency to require testing, Humble believes. He didn't do it back then, he said, because doing so would have stalled the rollout of dispensaries, which already been delayed due to litigation by former Governor Jan Brewer.
In the early days of the program, no laboratories existed to test marijuana, and it seemed possible that no lab would sign up for such a task while federal law still proscribed marijuana, he said.
"I would have been accused by the would-be new patients of purposely undermining the program by requiring testing that I knew couldn't be done," he said.
A mandatory testing program would likely raise the price of medical marijuana, which would have been another criticism by cannabis advocates, he added.
These days, though, the federal government — even with Jeff Sessions as Attorney General — takes no enforcement action against the medical-marijuana industry. On Sunday, Congress renewed the Rohrabach-Farr Amendment, which all but prohibits the spending of federal funds to stymie that industry.
Cannabis-testing firms have flourished in the new environment, especially where testing is mandated. Arizona has several testing firms that are primarily used by dispensaries to ensure competitive THC levels in buds.
Testing for contaminants isn't as common, since it's not required. Finding out that a batch of buds or edibles has high levels of pesticides could mean a monetary loss. Yet selling clean, quality products that keeps customers coming back is the goal of any competitive business.
Humble likens the situation to that of tattoo shops.
Arguably, tattoo shops could spread HIV, hepatitis, or other blood-borne pathogens if they reuse dirty needles. Humble said that while he was the ADHS director, he pondered the question of whether the shops should be regulated by the state for the good of public health. When he examined the evidence for signs of problems, though, he found none. By and large, he said, tattoo shops practice acceptable safety standards that don't leave their customers infected.
The same assumptions hold true for medical-marijuana dispensaries, too, he said.
Contaminants may show up in tests of cannabis. But if the presence of mold, pesticides, or other nasty stuff has hurt cannabis consumers, Humble pointed out, there's scant evidence of it.
"Where is the survey data that suggests this is a widespread public-health issue?" Humble said.
Humble pointed out, however, that increasing numbers of marijuana consumers or their children end up in emergency rooms these days not because of contaminants in their marijuana — but because of a bad reaction to the marijuana itself.
Noted Arizona marijuana researcher Dr. Sue Sisley agreed that the need for mandatory testing remains an open question.
Sisley is a proponent of standards, in general. She's a member of the Independent Laboratory Advisory Committee of Nevada, which set testing standards for that state's medical-cannabis program.
Nevada requires all dispensaries to test samples of their cannabis yield and report any failed tests to the state. The state forbids the stores from selling products with unacceptable levels of contaminants.
"I think we have found the right balance in Nevada which protects patient safety and still enables growers to successfully get medicine on shelves without exorbitant costs," she said. "We want to make sure that patients are not exposed to high levels of mold, microbials, nor other contaminants like heavy metals such as lead, etc., nor pesticides that could be toxic when heated or burned."
Sisley's the co-principal investigator in a groundbreaking study of the effects of cannabis on military veterans with post-traumatic stress disorder. In March, she accused the federal government of sending her moldy marijuana for the study from its farm at the University of Mississippi.
That's when she found out the feds have never tested its supposedly research-quality marijuana for mold since the farm first opened in 1968.
After Sisley's complaint to the press, the National Institute on Drug Abuse published a statement on its website about mold in marijuana, saying the issue would be studied further.
"There is currently no universally accepted standard for levels of mold and yeast on marijuana and different health organizations set cutoffs for acceptable levels spanning an enormous range," NIDA said. "In response, NIDA is conferring with the Food and Drug Administration (FDA) to determine what analyses and specifications are appropriate for NIDA-supplied marijuana."
Yet the fact is, Sisley said, no one knows what guidelines would be appropriate.
"If cannabis has mold present, is that really harmful to patients? Especially if they are smoking or vaporizing, are they burning off mold spores before it reaches human membranes?" Sisley wondered. "As a physician, I worry about sick patients receiving cannabis that has excessively high levels of mold, but we really don't understand what is the correct threshold that is safe."
She added that certain strains of mold are not pathogenic, meaning they're known to be harmless to humans.
Every sample of marijuana tested at Delta Verde Laboratory in north Phoenix comes back positive for mold or yeast, the lab's director and owner, Jim Clark, said.
"These organisms are ubiquitous," he said, adding that food also contains some detectable mold or yeast.
What counts is how much is present. Whether people get sick from moldy marijuana is another question. He's never heard of a case, he said.
Clark has previous experience working for the state DHS testing food and beverages. Analyzing medical marijuana, whether flowers, edibles, or concentrates, involves similar procedures.
Petrifilm, but hose tests aren't popular.
Two instruments do almost all of the testing at the lab — a high-performance liquid chromatograph (HPLC) and a gas chromatograph (GC). Test results are displayed on a computer screen. The machines determine the levels of the compounds expected to be in marijuana, like THC and CBD. Dispensaries use that information to inform and entice their customers, and to help cultivate the best yields.
For $50, the lab will provide the same test for individual patients who bring in samples.
Companies have become slightly more interested in testing for unusually high levels of pesticides, Clark said, but demand is still too low to buy another machine, even more expensive than the other two, that could do the job. Delta Verde is preparing to partner with an out-of-state company that can test for contaminants, though it can test for leftover residues from butane or other solvents often used in making concentrates like shatter in the GC.
Testing for metals like lead would require an additional machine.
Clark said he couldn't comment on whether most dispensaries in the state do a good job protecting their customers from poor-quality or contaminated products.
"The ones we work with, they're doing a good job," he said. "But that's not the majority of dispensaries."
Clark and his business partner, Mike Small, came up with the idea to start the business over a beer in 2014. They asked ADHS what they needed to do and were told there were "no requirements for a laboratory doing what we do," he said.
Naturally, Clark and Small believe in mandated testing, which would provide a boost for their business.
For the time being, the reports generated by Delta Verde and other cannabis-testing labs are given only to the dispensaries.
"It's in their hands," Clark said.