There is an economic argument, called the “Iron Law of Prohibition” that making a drug illegal should increase the potency of that drug. The primary empirical example is that during prohibition, smugglers mostly smuggled hard liquor because it was easier to smuggle.
Its true that prohibition increases transportation costs. But there are many other factors at work that make this far from an “Iron Law.” Aside from higher transportation costs, illegal markets should have higher capital and human resource costs. Mature capital markets and high human capital employees should not be as readily available to criminal enterprises. Funding crime is risky, so is engaging in it. 3rd party reviews of illegal goods should be more difficult to come by. If someone printed a guide to which dealers have the best cocaine in a city, law enforcement could use that to make a lot of arrests. So, information on what products are good or not is going to be less open and abundant. Finally, governments will not hold the sellers of illegal products to their claims. If your drug dealer of choice sells you some baking soda and tells you its cocaine, no judge or regulatory body will get you compensation.
The sum result of all these increased costs and decreased consumer protections should be that illegal markets are less efficient than legal markets. They should do a worse job of delivering consumers what they want. People want hard liquor and there are thousands of varieties available. But they also want beer and wine because the other things in the drink besides the alcohol are also desirable. In the case of wine, they are even considered healthy.
In the less efficient prohibition era market, all the nice forms of alcohol that people enjoy were harder to come by. This article explains that “Stolen and redistilled [industrial] alcohol became the primary source of liquor in the country.” So if you were drinking during prohibition you were probably drinking paint thinner, from which most of the toxins had hopefully been removed. And a lot of the time the toxins weren’t all removed (especially since the government demanded that more toxins should be added). So, the average concentration of alcohol increased during prohibition, but so did the amount of undesirable adulterants. The main effect was that variety and quality was reduced.
which would you choose?
Compare that to the case of marijuana. The other stuff in a marijuana flower is not good for anything. People like the THC (actually TCHA) and CBD to some extent. Everything else will just harm your lungs without any benefit. Since pot prohibition has been curtailed (though not completely ended yet) there has been more investment in developing hybrid strains with higher concentrations of THCA. There are independent labs that will verify the concentration of each strain and consumers can rely on those numbers. There are even more potent forms of consumer marijuana now, like dabbing. Does anyone think that if marijuana were totally legalized that THC concentrations would go down? As long as people prefer more potency, the drug will get more potent in a legal market.
You’re not getting a label like that from a drug dealer
People will also bring up the case of opiates and Fentanyl to make the case that prohibition increases potency. Fentanyl is very potent, in some ways, but “The biological effects of the fentanyl analogues are similar to those of heroin, with the exception that many users report a noticeably less euphoric high associated with the drug.” Since Fentanyl is less desirable than other opiates, it is often erroneously sold as heroin or mixed in with poor quality heroin. If recreational opiates were legalized, I don’t think we’d see a dramatic drop in potency. Addicts develop high tolerances, and they don’t want to have to do massive injections to get their fix. Instead, we’d probably see better purities, with less undesirable adulterants. Better labeling and more precise dosing. Theoretically, we could also see synthetic opiates developed that create more euphoria with less depression of respiratory drive, and maybe even less addictiveness. The best and brightest are not working on this problem because making the safest, most fun drugs possible is a very serious crime.
That last thought suggests a regulatory change that might make a big difference to the world. What if the FDA made a category for recreational drugs, and approved (without a prescription obviously) whatever available was most enjoyable with the fewest undesirable side effects. Is there any particular reason why people should not be able to take drugs for enjoyment if doing so harms neither themselves or others? Such a regulatory category would create incentives for real research to see what is possible. The existence of safe, non-addictive drugs that are more fun that alcohol or heroin (or even THC) could not only alleviate the current opiate epidemic, but all possible future drug epidemics.