When people talk about hallucinations, they usually think about wild visuals or sounds that feel strangely real. But behind all that, there’s a simple question: what chemical in the brain actually causes it? You might expect a single switch that flips everything on, but the truth is a bit more layered. The main player is serotonin, especially one of its receptors called 5-HT2A. When this receptor gets activated in certain ways, the brain starts connecting information differently, which can lead to hallucinations. It’s the same system that psychedelics like psilocybin interact with. Once you understand that, the whole idea of hallucinations becomes a little less mysterious.
How Serotonin Shapes Hallucinations
Serotonin is a chemical that helps manage mood, perception, and how we make sense of the world. When something strongly activates the 5-HT2A receptor, the brain starts firing in new and unpredictable patterns. That’s where hallucinations come from. One report put it simply: “Psychedelics engage serotonin receptors that alter how widespread brain networks communicate.”
That shift in communication can make thoughts blend together or visuals appear more vivid. It’s not random; the brain is just processing information in a different style than usual.
Why the Brain Starts Seeing Things
Hallucinations happen when the areas of the brain that handle vision, hearing, and imagination begin working together more loosely. Instead of filtering out extra information, the brain lets more signals come through. A medical source described it as the brain “misinterpreting internal signals as if they were coming from the outside world.”
That’s why someone might see patterns, colors, or shapes even with their eyes closed. The signals are coming from inside the brain, not from what’s in front of them.
Other Chemicals That Play a Supporting Role
Even though serotonin is the star, it doesn’t act alone. Researchers studying psychedelics noticed that several parts of the brain light up during hallucinations, showing that it’s a network effect, not a single spark. Some of the supporting factors include:
- Glutamate activity (linked to learning and memory)
- Dopamine shifts in certain pathways
- Reduced filtering in the thalamus
These secondary effects help explain why hallucinations can feel emotional, meaningful, or oddly symbolic.
Where Shrooms Fit In
Psilocybin, the active compound in magic mushrooms, turns into psilocin once it enters the body. Psilocin binds strongly to, you guessed it, the 5-HT2A receptor. That’s why psilocybin experiences can include visuals, unusual thoughts, or deeper emotional insights. One source summed it up nicely: “Classic psychedelics rely primarily on serotonin receptors but ripple across broader brain networks.”
It’s not just about seeing things. Many people describe a sense of clarity, connection, or introspection that comes from these brain changes. The hallucination part is only one slice of the experience.
Do Hallucinations Always Mean Psychedelics?
Not at all. The brain can create hallucinations for many reasons, including medical conditions, extreme stress, or even lack of sleep. The mechanism isn’t always identical, but serotonin and perception networks often show changes in all these situations. That’s why understanding the chemistry behind hallucinations helps doctors tell harmless experiences apart from ones that might need attention.
Summary
The chemical most responsible for hallucinations is serotonin, especially when the 5-HT2A receptor gets activated. This change affects how different brain networks talk to each other, which can make sights, sounds, and thoughts feel intense or unusual. Psilocybin connects to this same system, which is why magic mushrooms can trigger vivid or meaningful hallucinations. Even though serotonin is the main driver, other brain chemicals play smaller roles, making hallucinations a complex but fascinating experience.
Sources
Neuroscience News – More Than Serotonin: How Psychedelics Engage the Whole Brain
Medical News Today – What Really Happens in the Brain During a Hallucination?
Journal of Neuroscience – Beyond the 5-HT2A Receptor: Classic and Non-classic Targets in Serotonergic Hallucinogens