If you decide to drop acid, you’ll want to clear your schedule: A trip on lysergic acid diethylamide can last anywhere between six and 20 hours. Why acid trips last so long has been a mystery — until now. New research published Thursday in Cell explains that it all comes down to how LSD attaches itself to the brain cell’s serotonin receptors.

In a breakthrough experiment, scientists from the University of North Carolina School of Medicine successfully bound LSD to a human serotonin receptor and managed to crystallize them together through protein crystallography. This allowed them to observe what actually happens when the drug is actively exerting its psychedelia-inducing effects on a brain cell.

Here’s what they saw: When an LSD molecule encounters the receptor, part of the receptor folds over the molecule. The researchers compare this to the way a lid on a trash bin works — the presence of LSD triggers the receptor to close in and trap the molecule. An acid trip ends as the LSD molecules “pop off” these receptors, are sucked into the cell, and eventually are disassembled. This experiment also disproves the previous belief that LSD “washes” out of the fluid of the brain within four hours.

“We think this lid is likely why the effects of LSD can last so long,” lead author Bryan Roth, Ph.D., said in a statement. “LSD takes a long time to get onto the receptor, and then once it’s on, it doesn’t come off. And the reason is this lid.”

The orange bar is the "lid" that keeps LSD bound.
The orange bar is the "lid" that keeps LSD bound.

Instead of observing this happen in an actual brain, the researchers synthesized the serotonin receptors from lab cells, brought in the LSD molecules, and then froze the moment where the two interacted by turning them into a crystalized structure. It took the team two years to create one of these crystals — a discovery that allowed them to take an X-ray photo of the moment, leading them to the lid conclusion.

Roth says that this research allows scientists to have a better understanding of the structure of LSD and how it affects the brain, which in turn may lead to the development of therapeutic drugs that incorporate LSD. Other researchers have argued that LSD could be the solution to ailments like anxiety and addiction.

“I think it’s important for the pharmaceutical industry to understand that if you modify just one tiny aspect of any compound, you might affect the way it sits in the receptor,” co-author Daniel Waker, Ph.D., said in a statement. “But it could have potential medicinal uses, some of which were reported in the medical literature decades ago.”

Photos via UNC School of Medicine , Giphy