Yes, here is Keith Humphreys from Wonkblog:
Although some people believe prohibiting drugs is what makes their potency increase, the potency of marijuana under legalization has disproved that idea. Potency rises in both legal and illegal markets for the simple reason that it conveys advantages to sellers. More potent drugs have more potential to addict customers, thereby turning them into reliable profit centers.
In other legal drug markets, regulators constrain potency. Legal alcohol beverage concentrations are regulated in a variety of ways, including through different levels of tax for products of different strengths as well as constraints on labeling and place of sale. In most states, for a beverage to be marketed and sold as “beer,” its alcohol content must fall within a specified range. Similarly, if wine is distilled to the point that its alcohol content rises too high, some states require it be sold as spirits (i.e., as “brandy”) and limit its sale locations.
As states have legalized marijuana, they have put no comparable potency restrictions in place, for example capping THC content or levying higher taxes on more potent marijuana strains. Sellers are doing the economic rational thing in response: ramping up potency.
How about the Netherlands?:
The study was conducted in the Netherlands, where marijuana is legally available through “coffee shops.” The researchers examined the level of delta-9-tetrahydrocannabinol (THC), the main intoxicant in marijuana, over a 16-year period. Marijuana potency more than doubled from 8.6 percent in 2000 to 20.3 percent in 2004, which was followed by a surge in the number of people seeking treatment for marijuana-related problems. When potency declined to 15.3 percent THC, marijuana treatment admissions fell thereafter. The researchers estimated that for every 3 percent increase in THC, roughly one more person per 100,000 in the population would seek marijuana use disorder treatment for the first time.
The Dutch findings are relevant to the United States because high THC marijuana products have proliferated in the wake of legalization. The average potency of legal marijuana products sold in the state of Washington, for example, is 20 percent THC, with some products being significantly higher.
I believe that marijuana legalization has moved rather rapidly into being an overrated idea. To be clear, it is still an idea I favor. It seems to me wrong and immoral to put people in jail for ingesting substances into their body, or for aiding others in doing so, at least provided fraud is absent in the transaction. That said, IQ is so often what is truly scarce in society. And voluntary consumption decisions that lower IQ are not something we should be regarding with equanimity. Ideally I would like to see government discourage marijuana consumption by using the non-coercive tools at its disposal, for instance by making it harder for marijuana to have a prominent presence in the public sphere, or by discouraging more potent forms of the drug. How about higher taxes and less public availability for more potent forms of pot, just as in many states beer and stronger forms of alcohol are not always treated equally under the law?