Corva’s attack on cheating on marijuana plant testing

Testing companies gain customers if they can report falsely high THC in cannabis plants — and charge low prices. A friend says she quit the testing business because as an honest tester she was losing business to cheaters.

Thanks to Bob Young of the Seattle Times for brining Dr. Dominic Corva’s write-up to my attention.  (This blog doesn’t have enough readers to scoop him.)

My friend Dr. Corva looks at the cannabis testing problem in Washington.  His full write-up is here:

I think Dr. Corva is a smart and conscientious advocate and thought leader, and I’m always interested in what he is thinking.

Dr. Corva’s Proposal:

“Normalize lab results by lab, and require only the percentile of each result to be listed on the package rather than a precise percentage.”

He elaborates on the problem this way:

“Both of these problems create suboptimal public policy results, with respect to scientific accuracy, on the one hand, and unfair market advantage for untrustworthy labs on the other.”

He elaborates on his proposal this way:

“For a lab that consistently ranges up to 32% but no higher, for example, a sample that tests at 32% would be reported at the 100th percentile. The number on the package would be 100.

“For a lab that consistently ranges up to 25%, a sample that tests at 25% would also be reported at the 100th percentile. The number on the package would also be 100.”


I have this first reaction:

Dr. Corva’s proposal indeed addresses an unintended consequence:  A rule that is meant to inform and protect consumers instead misleads them.


  1. But would you need to add a rule banning labeling as to purported actual THC content – that is, banning labeling that is now required?  Otherwise, sellers could present normalized results, but also list (alongside those results)purported actual THC numbers,  but consumers might be led to think that all this seller’s products are high THC – even those in low percentiles.
  2. Is a ban on listing purported THC content constitutional?  Commercial free speech might say no.
  3. Are people comfortable that the mission of informing and protecting consumers can still be achieved with this method alone?  Do some sellers have product mixes that skew high or low?

That said, this is an idea worth thinking about more.  I can’t come up with an immediate problem with requiring normalized results (aside from general opposition to regulation).  I just don’t know that normalized results solve the problem totally.  But I am interested in hearing from Dr. Corva.  In any event, I think normalized results add valuable information for consumers.

More to come.


Another possible reaction to test-cheating is a stated THC tax.

This reaction gets easier to imagine as time goes on, for two reasons.

First, price per-gram will go down over time, so Washington’s percentage of price tax will decline for each gram of THC or gross weight.  Then the declining after-tax price will be hard for the black market to match if enforcement is adequate.  An add-on or alternative tax might not push too much commerce to the black market then.

Second, the state can take the time a bureaucratic government needs to start something new.

Here’s more:

Legible, formatted version at RAND Report, Considering Marijuana Legalization: Insights for Vermont and Other Jurisdictions,, p. 84.


The serious issue for the integrity of testing is pesticides.  Poison that kills insects is usually no good for humans.  Maybe checking labs by monitoring results randomly after the fact can go a long way toward solving this problem — if the allowed amount is zero.




One thought on “Corva’s attack on cheating on marijuana plant testing”

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