This is a rather new word, which apparently means "substances which cause/enable molding of the mind," i.e., from my perspective, "brainwashing drugs."
It is mostly synonymous with "psychedelics" but implies a bit of materialistic brain theory (perhaps "dendrite manifesting" instead of the older and more romantic "mind manifesting"). According to Wikipedia, it was coined in 2019 by David E. Olson, a professor of chemistry, biochemistry and molecular medicine at UC-Davis.
When I first encountered the word in an opinion piece in JAMA Psychiatry, I vaguely recognized the bio-implication but immediately wondered why anyone needed a new word to replace Humphrey Osmond's venerable old "psychedelics." There might be various explanations. Maybe the medical profession wants or needs to separate itself from the history of 60's craziness. They'd love people to think that if they use LSD, it will be in connection with careful, scientific research, not at all like those reckless adventures of Ken Kesey and Timothy Leary. If they do push such a brand, it will be a lie of the same magnitude as the "chemical imbalance" myth.
Kesey and Leary only pushed acid into mainstream America a decade after it had been thoroughly researched in very well-funded government programs, designed with the successful precedent of the Manhattan Project firmly in mind. The researchers of the 1950's abandoned psychedelics for the simple reason that unlike with the nuclear weapon experience, they discovered they could not control any aspect of these drugs. They couldn't control the effect of LSD on any particular person at any particular time, and they couldn't control the market supply or (most surprisingly to themselves) the demand. The central message of LSD was simply, no control.
Merely calling psychedelic drugs "psychoplastogens" will never change the essential reality of no control. "Bad trips" will happen at about the same frequency as they did in the Haight in 1967; inspired musicians and tech engineers, micro- or mega-dosing, will imagine "enhanced creativity" only to burn out far too quickly; and here or there we will see a new Charlie Manson horror story, or a new Richard Helms atrocity.