Testing illegal drugs for the active ingredient differs from testing for poisonous adulterants. Both tests have opposite effects on drug use before and after buying. After the pill has been purchased, testing reduces use, because sometimes the drug fails the test, whether correctly or not, and is discarded. Before purchase, the option to test for and avoid adulterated or inactive drugs reduces the buyer’s risk, thus increases use.
In the longer term, testing benefits the dealers of purer, more predictable and less toxic drugs, putting some suppliers of fakes out of business. Pill predictability reduces overdoses – a health effect similar to lower toxicity. If old drugs can be tested, but new ones not, then buyers experiment less and the incentive to invent new narcotics decreases.
The avoidance of poisonous adulterants is good for public health, but purer pills not necessarily so. Inactive drugs undermine consumer confidence in the illegal market, reducing use, prices and casual purchases. Trust then requires a long-running relationship with the seller, which has multiple benefits. It motivates dealers to care about the health of their loyal customers, simplifies policing and gives researchers and social workers better long-term access to the at-risk population.
One claimed benefit of party drugs is that they reduce anxiety, increase the user’s confidence and social interaction, thus improving mental health. Evidence from psychiatric medicines suggests that many such benefits are due to the placebo effect. Users are quite inaccurate in estimating the purity of ingested drugs, and factors like price and place of purchase strongly influence their perception of purity. The price per pure gram is negatively related to purity in some markets, further supporting the placebo interpretation. If inactive pills boost confidence similarly to illegal drugs, then there is a clear case for flooding the market with harmless placebos. The availability of pill tests for the active ingredient reduces this opportunity to make the illegal market inefficient. Tests for toxic adulterants, however, actually favour harmless placebos.