The team says the discovery could lead to the development of better treatments for mental health disorders including depression, addiction and post-traumatic stress disorder (PTSD).
Depression has long been believed to be associated with an imbalance in brain chemicals. However, recent studies have shown that structural changes also play a role.
One 2017 study from Harvard Medical School found that the hippocampus - which is responsible for processing memory and emotional responses - is nine to 13 percent smaller in those suffering from depression.
The study's authors explain that this doesn't mean neurons die off in depressed people. Instead, neurites, the sections that bridge out and connect to other neurons, retract.
These tiny fragments, known as axons and dendrites, facilitate communication at synapses, or connections between brain cells.
Senior author Dr David Olson, an assistant professor of chemistry at UC Davis, explained that shriveled up neurites in the prefrontal cortex - a key brain region that regulates emotion, mood, and anxiety - is 'one of the hallmarks' of depression.
These brain alterations also appear in cases of anxiety, addiction and PTSD.
'People have long assumed that psychedelics are capable of altering neuronal structure, but this is the first study that clearly and unambiguously supports that hypothesis,' he said.
The researchers, led by Dr Olson, specifically analyzed ecstasy, LSD, and hallucinogenic designer drugs DMT and DOI.
'These are some of the most powerful compounds known to affect brain function. It is very obvious to me we should understand how they work,' Dr Olson said.
In past research, Dr Olson and his team showed that doses of DMT helped rats overcome fear to the memory of a mild electric shock, which could help design treatments for PTSD.
In this study, rats were treated with a single dose of DMT, a psychedelic compound found in the Amazonian herbal tea known as ayahuasca.
While the drug was eliminated within an hour, the 'rewiring' effects on the brain could be seen 24 hours later, demonstrating that these effects last for some time.
Dr Olson compared the effects of the psychedelics to ketamine, another illicit drug which has appeared to be a breakthrough psychiatric treatment for severe depression, relieving patients' moods much faster than traditional antidepressants.
The researchers found that many psychedelics had equal or greater on neural plasticity, or brain growth.
The psychedelics made both dendritic spines and synapses denser. Some, including LSD, were even more potent and effective than ketamine in boosting the growth of neurites.
