According to this article Joe Biden says we should postpone federal legalization of marijuana until we have more scientific evidence about the degree to which it acts as a "gateway" drug.
The term "gateway drug," in ordinary usage, seems to imply that some drugs possess a property such that users of those drugs will tend to move on to other more dangerous drugs over time. We might expect this of opioids, where a patient who likes the effects of an opioid prescribed for a legitimate medical purpose, but loses their source, seeks similar drugs on the black market, or a person addicted to heroin uses fentanyl.
Biden seems to suggest that the drug itself possesses this property, but in my opinion the risk may lie, not in the drug itself, but in the circumstances surrounding how or where the user obtains the drug. Obtaining a drug on the black market may expose the user to other, more dangerous, drugs available from the same dealer or his/her contacts. Legalizing marijuana might, over time, actually reduce the exposure of marijuana users to other drugs.
Scientists cannot easily design experiments with legality as a variable. We may have to move forward with legalization and see what happens, it may take many years to reach for all the social pressures to stabilize.
Biden, among others, also seems to ignore the gateway potential for two legal, but deadly, drugs: How many individuals have proceeded to use of "harder" drugs without having first used legally available tobacco and/or alcohol?
Perhaps we will only reduce the harm associated with the gateway process by minimizing the economic forces that support the black market, that is by legalizing all drugs.
Berry Edwards, MD