At Washington Post Wonkblog, Christopher Ingraham notes that the potency of available marijuana has been increasing:

Retail outlets in Denver and elsewhere advertise strains that contain 25 percent THC or more. As legalization opponents are forever fond of saying, this isn’t your daddy’s weed.

There is extensive evidence available to support Christopher’s observation about rising marijuana potency. But I am not sure that his causal explanation for the potency increase comports with the facts. He attributes it to prohibition and believes therefore that legalization will reverse the trend:

As prohibition eases and legal markets open up, growers now have the breathing room to select for traits beyond high THC content. Demand from new users looking to experience a social high, rather than four hours of couch lock, will likely drive this. The end result may be a resurgence of milder strains of weed that are more akin to fine wines than to bathtub gin.

There are a couple analytic problems here. First, over the past 5-10 years, legalized marijuana markets (medical and recreational) have expanded dramatically and marijuana enforcement has dropped sharply, but as the data Christopher himself presents show, potency went up rather than down during that time. Second, if one looks at other legal industries that sell psychoactive drugs, they typically do anything they can to give customers as much potency as possible for every dollar they take in.

For example, the British alcohol industry has been warring with the government from at least 1751 (e.g., The Gin Act) to the present day (e.g., minimum unit pricing) over the former’s efforts to churn out cheap, high potency alcoholic beverages. Even if one restricts analysis to the “fine wine” analogy that Christopher evokes, it has to be said that over the past quarter century, the alcohol content of wine sold in the U.S. has crept up from the 8-10% range to 12-14%.

For drug producing industries, higher potency products are a good. They lower transport costs because the product has less mass and weight. Consumers like getting more bang for the buck. Finally, higher potency products are more addictive, and addicted customers are the best customers. I can’t stress strongly enough that all these advantages accrue to both legal and illegal drug sellers. There is nothing in the legalization of drug-producing industries that eliminates these financial incentives and because they can operate openly, such legal sellers actually may be better at achieving a saturation of lower cost, high-potency products in a market than are sellers constrained by prohibition.

People who enjoy the occasional low potency marijuana cigarette tend to assume that sellers have a big economic interest in catering to them. But about 90% of the weed being sold in Colorado is used by people who smoke every day or almost every day. There just isn’t as much money in the “fine wine” set of occasional marijuana users as there is in daily, physically dependent users of high-strength pot.

A legal market thus doesn’t inherently bring us low potency. Rather, it brings us a fight between regulators who generally want low potency products to dominate the market and sellers who generally want high potency products to dominate the market. Sometimes the regulators win, sometimes the industry does. When the industry wins, higher potency products are more available than they are under prohibition. When the regulators win, industries are forced against their economic interests to produce more of the lower potency products that Christopher and I agree pose less risk to consumers.