Psychedelics, BDNF & Psychoplastogens

For a century we described what psychedelics do to experience — the visions, the dissolved self, the sense of revelation. Only recently have we been able to watch what they do to tissue. And the picture that has emerged from the microscope is, if anything, more astonishing than the subjective reports: these molecules make the brain physically grow. New branches reach out from neurons, new connection points bud along them, the architecture of thought itself remodeling in real time. This is the story of the molecular machine underneath every article in this journal — the machine called neuroplasticity, and the fertilizer, BDNF, that runs it.

What the microscope revealed

The landmark demonstration came in 2018, when Calvin Ly, David Olson and colleagues published a paper with a title that says it all: Psychedelics Promote Structural and Functional Neural Plasticity. Working in rodent and even fly neurons, they showed that a range of psychedelics — LSD, DMT, DOI and others — increased the density of dendritic spines (the tiny knobs where synapses form), promoted the growth of new neurites (the branches themselves), and strengthened synaptic connections (Ly et al., 2018). The effect was fast and it was potent, rivaling ketamine, the fast-acting antidepressant that first alerted science to the healing power of rapid plasticity. For a field long focused on the felt experience, this was a shift of ground: the drugs were doing something concrete, physical and measurable to the wiring of the brain.

BDNF: the brain’s fertilizer

Pull the mechanism apart and one molecule sits at the center: BDNF, brain-derived neurotrophic factor. If neurons are plants, BDNF is the fertilizer — the signal that tells them to grow, branch, form new synapses and survive. Psychedelics, acting through the 5-HT2A receptor, trigger a release of BDNF, which binds its receptor TrkB and switches on mTOR, the master controller of the protein-building that physically constructs new synapses. The chain is 5-HT2A → BDNF → TrkB → mTOR → new synapses. And the proof that this chain is essential is elegantly direct: when researchers block BDNF signaling, or TrkB, or mTOR, the plasticity collapses — the drug loses its power to grow neurons. This is the same pathway ketamine uses, which is why classic psychedelics and ketamine, chemically unrelated, converge on the same rapid healing.

Why this matters for depression

Here the molecular story meets human suffering. A leading modern theory of depression is the atrophy hypothesis: chronic stress and depression are associated with the retraction of dendrites and the loss of synapses in the prefrontal cortex and hippocampus — the brain literally pruning back its own connectivity in the regions that regulate mood. If depression is in part a disease of lost connections, then a molecule that rapidly regrows them is aiming straight at the root. That is exactly what psychoplastogens appear to do: within a day of a single dose, the withered branches begin to bud again. It reframes the antidepressant effect seen in psilocybin trials not as a mood tweak but as structural repair — and it fits the afterglow window, the open, malleable period after a session when the freshly grown circuitry can be reshaped by new experience.

Olson’s big idea: psychoplastogens

In 2018, David Olson gave this whole class of molecules a name and a mission. A psychoplastogen, in his coining, is any compound that produces rapid, robust promotion of neural plasticity after a single exposure. It is a deliberately broad tent — it includes classic psychedelics, ketamine, and MDMA, uniting chemically diverse drugs by what they do to neurons rather than how they feel. The reframing is powerful because it turns a fuzzy question (“how do trips heal?”) into a sharp, druggable one (“how do we safely maximize plasticity?”). It also sets up the most provocative question in the field — if the healing is the plasticity, and the plasticity is molecular, then do you need the hallucination at all?

Tabernanthalog: healing without the trip

Olson’s lab answered that question with chemistry. Starting from ibogaine — a powerful but toxic and hallucinogenic plant psychedelic — they engineered a stripped-down analog they called tabernanthalog (TBG). In a 2020 Nature paper, TBG proved to be non-hallucinogenic and non-cardiotoxic, yet it still promoted structural neural plasticity, reduced alcohol- and heroin-seeking behavior, and produced antidepressant-like effects in animals (Cameron et al., 2020). In other words: they kept the rewiring and removed the trip. This is the frontier that has drawn enormous pharmaceutical interest — a new generation of non-hallucinogenic psychoplastogens that could deliver the structural healing of a psychedelic as an ordinary take-home pill, no clinic, no journey, no risk of a bad one. Whether that fully works is one of the great open experiments of the decade.

The honest limits — and the open debate

Two cautions, and one genuine controversy. First, almost all the structural evidence — spines, neurites, BDNF blockade — is from animals and cultured neurons; measuring real-time synapse growth in a living human brain is extraordinarily hard, though early imaging hints line up. Second, plasticity is not automatically good — it is a capacity for change, and change can go either way; the new wiring still has to be shaped by a healthy context, which is why integration matters. And the controversy: the tabernanthalog result has reopened a fierce debate about whether the subjective experience is truly dispensable. Some researchers argue the plasticity is the medicine and the trip is a side effect; others insist the felt experience — the meaning, the catharsis, the mystical sense — is doing essential therapeutic work that no pill can replace. The honest answer is that we don’t yet know. What is settled is remarkable enough: psychedelics are among the most powerful plasticity-promoting molecules ever found, they work through the BDNF-TrkB-mTOR engine, and understanding that engine is rewriting psychiatry from the synapse up.

OOTW Journal is educational and does not provide medical advice. Psychedelics remain controlled substances in most countries and are not safe for everyone, including people with a personal or family history of psychosis or bipolar disorder, and those on serotonergic medications. Nothing here is a recommendation to use any psychedelic. If you are struggling with your mental health, please reach out to a qualified professional.