Biology: To what extent do serotonergic psychedelics promote neuroplasticity and mental health outcomes in adults?

Note: The following article was written by Aakifuddin Mohammed U6

Serotonergic psychedelics have returned to psychiatric research after decades of being associated mainly with counterculture and criminalisation. Substances such as psilocybin, LSD and DMT are now being investigated for their possible use in treating conditions including depression, anxiety, PTSD and addiction. Part of this renewed interest comes from the limitations of current treatments, especially for patients who do not respond well to conventional antidepressants.

One reason psychedelics are particularly interesting is their possible effect on neuroplasticity, the brain’s ability to reorganise itself and form new neural connections. If psychedelics can temporarily make the brain more adaptable, rigid patterns of thinking associated with some mental illnesses may also become easier to change. However, showing that a drug makes the brain more plastic does not necessarily mean that it improves someone's mental health. The more important question is whether these changes in the brain actually lead to meaningful and lasting improvements.

Psychedelics such as LSD, psilocybin and DMT act mainly on the serotonin 5-HT2A receptor. These receptors are common in areas of the brain involved in higher-order thinking and self-awareness, both of which can be affected in conditions such as depression and anxiety. Activating them also influences glutamate, a neurotransmitter involved in learning, memory and synaptic plasticity.

One theory suggests that psychedelics temporarily disrupt fixed patterns of brain activity, allowing communication between different regions to become less restricted. This could be useful in depression, where people can become trapped in repetitive patterns of negative thinking or rumination. By making these patterns temporarily less rigid, psychedelics may allow different perspectives to emerge. However, greater flexibility is not always helpful. Disrupting normal patterns of brain activity can also be distressing, meaning the environment and support surrounding the experience are likely to be important.

There is also evidence that psychedelics can physically affect connections between neurons. Laboratory studies have found increases in dendritic branching, dendritic spine growth and the formation of new synapses after exposure to certain psychedelics. These substances have also been linked to brain-derived neurotrophic factor (BDNF), a protein involved in the growth and survival of neurons. Together, these findings suggest that psychedelics can promote neuroplasticity at a biological level.

The main problem is that much of this evidence comes from animals or cells grown in laboratories. A neuron developing more connections does not automatically mean that a person will become less depressed or anxious. Evidence from humans is therefore much more important when considering whether these biological effects have any real therapeutic value.

Human studies have begun to provide encouraging results. Brain imaging following psilocybin therapy has shown increased communication between networks that would normally be more separated, alongside improvements in depressive symptoms. Clinical studies have also reported substantial reductions in depression and anxiety after psilocybin treatment, with some improvements continuing beyond the immediate psychedelic experience. Although this does not prove that neuroplasticity caused the improvement, it suggests that changes in brain function can occur alongside meaningful changes in mental health.

One possible explanation is that psychedelics create a temporary window of increased plasticity. During this period, established patterns of thought may become easier to change, allowing therapy or new experiences to have a greater influence. In this sense, the psychedelic may not directly “fix” depression. Instead, it could create a period in which psychological change becomes easier to achieve.

This raises an important question about what actually causes the therapeutic effect. It may be the biological changes taking place in the brain, but the psychedelic experience itself could also be important. Emotional insights or changes in perspective during treatment may help someone reconsider established ways of thinking. The most convincing explanation may therefore be that both work together: neuroplasticity makes the brain more open to change, while experience and therapy influence what that change becomes.

There are still reasons to be cautious. Many psychedelic studies involve relatively small and carefully selected groups, meaning their findings may not apply to everyone with a mental health condition. Placebo-controlled trials are also difficult because psychedelic effects are noticeable, so participants can often work out whether they received the active drug. Their expectations could therefore influence the results. Patients also usually receive preparation, professional supervision and therapy afterwards, making it difficult to separate the effect of the psychedelic itself from the support surrounding it.

There is also limited evidence about what happens over several years. Short-term changes in brain activity and symptoms are promising, but an effective psychiatric treatment needs to provide benefits that last while keeping risks acceptable. Larger studies involving more varied groups of people and longer follow-up periods are therefore needed.

Overall, the evidence suggests that serotonergic psychedelics can promote neuroplasticity and may improve mental health outcomes, particularly in depression and anxiety. Their effects on serotonin receptors, neural communication and the physical connections between neurons provide a convincing biological explanation, while early human research suggests improvements in both brain function and symptoms. What remains less certain is whether neuroplasticity itself is responsible for these improvements.

This brings the argument back to its starting point: making the brain more plastic is not automatically the same as making the mind healthier. Psychedelics appear to make established neural and psychological patterns temporarily less fixed, but what happens during that period may be just as important as the biological change itself. Their real therapeutic potential may therefore lie in opening a window for change, rather than producing that change on their own.