What Does LSD Do to Your Brain? (Why It Lasts for Hours)

LSD acts mainly on the serotonin 2A receptor, a protein on brain cells, and it changes how brain areas work together. Its effects can continue for many hours because LSD leaves this receptor very slowly and the liver needs time to change it.

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This article explains science. It is not medical advice and not a guide to drug use. If you have questions about LSD and your health, speak to a doctor.

Why can people see pictures with their eyes closed?

When you close your eyes, you see no picture of the room around you. Your eyes send almost no image to the brain.

In a 2016 study, volunteers on LSD reported vivid pictures with their eyes closed. No picture came from their eyes. So the pictures had to come from activity inside the brain.

Brain scans in the same study showed where this activity was. The scans also showed a change in the sense of self. This article follows the path of one molecule from a capsule to the brain. Then it returns to the scan results.

How did the story of LSD start?

The story starts in 1938 at the Sandoz company in Basel, Switzerland. The chemist Albert Hofmann worked with compounds from ergot. Ergot is a fungus that grows on rye and other cereal plants.

Hofmann wanted a medicine that could help blood circulation and breathing. He made a series of compounds from lysergic acid, a chemical from ergot. His 25th compound in this series got the name LSD-25.

The first animal tests did not show a useful medicine. So the company stopped the work, and the compound stayed on the shelf for five years. In 1943, Hofmann made LSD again.

On 16 April 1943, he felt unusual effects at work. Nobody knows how the chemical first entered his body. On 19 April, he took LSD on purpose to test it.

Because of the war, he could not get a car. So he rode home on his bicycle. People now call that day Bicycle Day. Today, scientists can measure where LSD goes in the body.

How does LSD reach the brain?

In some research trials, volunteers swallow LSD in gelatin capsules. Gelatin dissolves in the warm, wet stomach. Then the capsule releases the LSD.

The LSD moves through the wall of the gut into the blood. The blood carries LSD around the whole body. In one study, scientists estimated that about 71% of swallowed LSD reached the blood.

The brain has a barrier between the blood and the brain tissue. This blood-brain barrier controls which molecules can enter the brain. Animal studies suggest that LSD passes this barrier easily. Scientists have no matching measurements from human brain tissue.

In studies with people, the first effects started about 30 to 45 minutes after intake. In a study of 16 healthy volunteers, the level of LSD in the blood was highest after about 1.5 hours. The time differed from person to person.

Which receptor does LSD use?

A receptor is a protein on a cell. It responds to certain chemical signals. In the brain, LSD acts mainly on the serotonin 2A receptor. Its scientific name is 5-HT2A.

Serotonin is a messenger chemical that nerve cells use. It is the normal signal for this receptor. Part of the LSD molecule has the same ring shape as serotonin. Chemists call this ring an indole ring.

This shared shape can help LSD to fit into serotonin receptors. But the shape alone does not explain everything. The pocket of the receptor and other parts of the LSD molecule also matter.

LSD attaches to the receptor, and then LSD activates it. In tests with rat brain cells, LSD did not give the full response that serotonin gives. Scientists call a molecule with this weaker maximum response a partial agonist.

Scientists also tested this link in people. In a controlled study, they gave volunteers a drug that blocks the 5-HT2A receptor before LSD. Then LSD had much smaller effects on the volunteers' experience.

This result shows that the 5-HT2A receptor is very important for the effects of LSD. But LSD also attaches to other receptors, for example some dopamine receptors. These other targets may add to its effects.

Why do the effects last for hours?

The effects of LSD can continue for up to about 12 hours. In a study of 27 healthy volunteers, the effects lasted about 8.5 hours on average. The range went from about 5 to about 13 hours.

In laboratory tests, LSD leaves its receptor very slowly. In 2017, scientists made a 3D map of LSD inside a serotonin receptor. They used a method that shows the position of each atom.

The map shows a part of the receptor that folds over LSD. The scientists call this part a lid. The lid sits at the entrance of the pocket. Computer models suggest that it holds LSD inside.

Then the scientists changed one small part of the lid. This change made the lid move more freely. After this change, LSD left the receptor much faster.

The 3D map came from a related receptor, 5-HT2B. The scientists also measured how slowly LSD leaves 5-HT2A, and they tested the lid there too. So the lid is a good explanation for slow release, but it is not an exact clock for human effects.

The level of LSD in the blood also matters. The next sections show how the body removes LSD.

How does the body remove LSD?

The blood also carries LSD to the liver. In the liver, enzymes change LSD into other molecules. An enzyme is a protein that changes one chemical into a different chemical.

The kidneys then move some of these products from the blood into the urine. The main product in urine has the name 2-oxo-3-hydroxy-LSD. It has a much weaker effect on serotonin receptors, and scientists think that it is inactive.

In one study, only about 1% of the swallowed LSD left the body in urine without a change. About 13% left as the main product within 24 hours. The liver changes almost all of the LSD.

In the study of 16 volunteers, the level of LSD in the blood fell by half in about 3.6 hours. Scientists call this time the half-life. The effects became weaker together with the level of LSD in the blood.

Why do the effects last longer in some people?

Several liver enzymes work on LSD. One of them has the name CYP2D6. Genes carry the instructions to make enzymes, and people carry different versions of the CYP2D6 gene.

Some gene versions give a person no working CYP2D6. A 2021 analysis combined data from 81 healthy volunteers in four studies. Seven of them had no working CYP2D6.

In these seven people, LSD stayed in the blood for a longer time. The amount of LSD in their blood over time was about 75% higher. Their effects also seemed stronger and longer.

But the group had only seven people. So the result is not certain. It does not let anyone predict the effects for one person.

What did the brain scans show?

Now we return to the 2016 study from the start. A team from Imperial College London and the Beckley Foundation enrolled 20 healthy volunteers. Not every scan from every volunteer was usable.

Each volunteer received LSD on one day and a placebo on a different day. A placebo has no active drug in it. This design let the team compare each brain with itself.

The team measured each brain in three ways. One method measured blood flow. A second method followed changes in blood oxygen, an indirect sign of activity. A third method recorded very small magnetic signals from nerve cells.

With eyes closed, LSD increased the blood flow in the visual cortex. The visual cortex is the main vision area of the brain. More blood flow often goes with more activity.

The magnetic signals showed a weaker alpha rhythm in this area. Alpha is a brain rhythm of about 8 to 12 waves per second. It is usually strong when a person rests with closed eyes.

The visual cortex also worked together with many more brain areas than normal. When these changes were stronger, the volunteers reported stronger visual pictures. This link suggests that the pictures came from activity inside the brain, not from the eyes.

What happens to brain networks?

The brain has networks. A network is a group of brain areas with activity that rises and falls together. These connections are patterns of activity. They are not new nerve fibres.

With LSD, some networks became less separate from each other. But inside some networks, the usual connection became weaker. Scientists call this a change in network integration and segregation.

Think of a company. Each team usually talks mostly inside its own group. Now all the teams start to talk to each other more. Information can move between the teams in new ways.

This example only explains the pattern. It does not measure intelligence or health. A later study found that a 5-HT2A blocker prevented these changes in brain connections.

How can the sense of self change?

The scans also showed a link with the sense of self. One connection between two brain areas became weaker. The two areas are the parahippocampus and the retrosplenial cortex.

The parahippocampus lies on the inner side of the temporal lobe, near memory areas. The retrosplenial cortex lies deep in the middle of the brain.

When this connection became weaker, the volunteers reported a stronger loss of their sense of self. The researchers call this experience ego dissolution. This result shows a link. It does not show that these two areas contain a person's identity.

Does LSD affect every person in the same way?

LSD does not have the same effect on every person. The changes can feel pleasant. They can also cause fear, anxiety, confusion and panic.

Health agencies also list impaired judgement and a risk of psychosis in people with that vulnerability. Some people later have repeated changes in vision that cause distress. Doctors call this hallucinogen persisting perception disorder.

That is one reason why research trials select their volunteers with care. Research guidelines say that trials should not include people with a personal or close family history of psychosis.

A trained team stays with each volunteer for the full session. Results from these careful trials do not apply to use outside research.

Can LSD help in medicine?

Scientists now test a medicine form of LSD for anxiety. In 2025, the journal JAMA published a trial with 198 adults with generalised anxiety disorder.

This mid-stage trial compared several groups with a placebo group. In some groups, the anxiety decreased more than in the placebo group. The trial also reported unwanted effects, such as visual changes and nausea.

In September 2026, the company that develops this medicine reported positive results from a phase 3 trial in anxiety. A company report is not the same as a peer-reviewed paper.

The company plans to send its application to the US Food and Drug Administration in the first half of 2027. Today, it is not an approved medicine. It is still in research.

What this means

LSD moves from the gut into the blood, and then into the brain. There it attaches mainly to the 5-HT2A receptor. A lid on the receptor may hold LSD for a long time.

In the brain, some connections become stronger and others become weaker. The vision area works with many more areas, and this link matches the pictures that people see with closed eyes.

Later, the liver changes LSD into other molecules. Genes for liver enzymes can change how long LSD stays in the blood.

These findings come from small, controlled studies. They explain mechanisms. They do not make LSD safe, and they do not predict the effects for one person.

FAQ

Why does LSD last so long?

Two reasons work together. LSD leaves the 5-HT2A receptor very slowly, possibly because a lid on the receptor holds it. The liver also needs hours to change LSD, and the level in the blood falls by half in about 3.6 hours.

Which receptor does LSD act on?

LSD acts mainly on the serotonin 2A receptor, 5-HT2A. A drug that blocks this receptor made the effects of LSD much smaller in a controlled human study. LSD also attaches to other receptors.

Do the pictures with closed eyes come from the eyes?

No. Brain scans showed more blood flow and more connections in the visual cortex. Stronger changes went with stronger reported pictures, so the pictures came from activity inside the brain.

Is LSD an approved medicine?

No. A medicine form of LSD is in trials for generalised anxiety disorder. The company plans to apply to the US Food and Drug Administration in 2027, but no approval exists today.