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The Effects of Hallucinogenic Drugs on The Brain

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Biology 202
1998 First Web Reports
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The Effects of Hallucinogenic Drugs on The Brain

Alicia Ebbitt

Hallucinnogenic Drugs alter a person's perceptions of reality and may cause hallucinations and other alterations of the senses. Drugs classified as hallucinogens include: LSD (lysergic acid diethylamide), 2,5-dimethoxy-4-methylamphetime(DOM), N,N-dimethyltrptamine(DMT), psilocin, and mescaline. There are two aspects of these drugs that classify then as hallucinogens. They all have common side effects, including distortion of sensory perception, and other psychic and somatic effects. These drugs also exhibit cross-tolerance. This means that a user of hallucinogenic drugs develops a higher tolerance to hallucinogens, the more they are used and the shorter the time span is between the last usage.

Hallucinogenic drugs have been used throughout history for a number of reasons. They have been used as medicinal agents as well as having served religious purposes. Hallucinogens such as mescaline have been used in Native American ritual ceremonies. There was extensive usage of hallucinogens in the 60's and 70's as part of the counter- culture hippie movement. During the "acid tests" of this era, hallucinogenic drugs were used for mind exploration (B.L. Jacobs, "How Hallucinogenic Drugs Work").

Hallucinogenic drugs cause both physical and psychological effects on humans. The physical effects of these drugs include: dilated pupils, elevated body temperature, increased heart rate and blood pressure, appetite loss, sleeplessness, tremors, headaches, nausea, sweating, heart palpitations, blurring of vision, memory loss, trembling, and itching. A user of hallucinogenic drugs will also experience a number of psychological alterations in the brain. These drugs may cause hallucinations and illusions as well, as the amplification of sense, and the alterations of thinking and self-awareness. It is quite possible to have a bad reaction to hallucinogenic drugs. This is referred to as a "bad trip" and may cause panic, confusion, suspicion, anxiety, and loss of control. The long-term effects of these drugs can be quite dangerous. These long-term effects may include: flashbacks, mood swings, impaired thinking, unexpected outbursts of violence and eventually possibly depression that may lead to death or suicide.

Quite a lot of interest concerning hallucinogens has been generated by neurobiologists and other scientists. The effects that hallucinogenic drugs have on the brain are quite complicated and very interesting. Many users of hallucinogenic drugs have experienced whole personality changes which raises questions about the relationship between brain and behavior. Scientists are also curious as to how total alterations of the senses can occur as the result of hallucinogen usage. Many people that have used hallucinogens claim to have "seen sounds" or "heard colors". Scientists ask questions such as: How can a person under the influence of hallucinogenic drugs see things that aren't there? or How do flashbacks work? Another aspect of hallucinogenic drugs that interests scientists is that they are psychomimetic meaning that they mimic certain aspects of psychosis. Through the use of hallucinogenic drugs, one can induce temporary symptoms of psychosis.

As a result of the great interest in hallucinogens, many years of research have been done to try and determine exactly how the brain is affected by these drugs. Scientists have tried to determine if there is a specific site in the brain where hallucinogens act. This has been difficult to determine. Scientists still are unable to answer all questions about hallucinogenic drugs. However they have been able to determine certain areas of the brain that these drugs do act upon.

Early on in the reasearch on hallucinogens, it was determined that hallucinogenic drugs structurally resemble serotonin (5-HT) Serotonin is found in specific neurons in the brain that mediate chemical neurotransmission in the brain. Neurons containing serotonin can be found in the brain stem section of the brain. Axons of serotonergic neurons project to almost every part of the brain, affecting and communicating with all sections of the brain. Serotonin also acts at many receptor areas of neurons. Because hallucinogenic drugs are structurally similar to serotonin, it was theorized that hallucinogenic drugs may act upon serotonergic neurons (B.L. Jacobs, "How Hallucinogenic Drugs Work").

Scientists began to carefully study the serotonin system and found out that hallucinogens do in fact have some kind of effect on serotonin. Hallucinogenic drugs cause an increase in the level of brain serotonin, but they inhibit the rapid firing of neurons containing serotonin. This is a negative feedback system in which as the serotonin level rises, the activity of serotonergic neurons decreases. It was originally theorized that this effect of hallucinogenic drugs directly caused sense alteration and hallucinations. Several observations however have shown this theory not to be true. These observations include the following: Low doses of LSD effect behavior, but do not depress firing of serotonergic neurons, The behavioral effects of LSD outlast the alteration of the firing of the serotonergic neurons, Repeated dosage of LSD results in a decrease of behavioral changes, but still effects neuron firing, Other hallucinogens do not affect serotonergic neurons, When serotonin levels are depleted, the effectiveness of LSD is not eliminated (Ian Leicht, "Postulated Mechanisms of LSD").

It has now been determined that the effects of hallucinogenic drugs are actually caused by the effects that hallucinogenic drugs have on the post-synaptic activity of serotonergic neurons. Hallucinogenic drugs directly affect the serotonin receptors(specifically the serotonin receptor subtype, 5-HT2), which is what eventually results in a complex pattern of action potentials and activity. This was proven by the fact that the depletion of serotonin levels in animals does not result in a decrease of behavioral effects caused by hallucinogenic drugs (B.L. Jacobs, "How Hallucinogenic Drugs Work").

Hallucinations and other effects of hallucinogens are however very complicated experiences. They are not simply a part of a cause and effect system in the brain, where hallucinogenic drugs act on serotonin and cause hallucinations. Instead, hallucinogenic drugs act initially on the serotonin system, which sends into motion, a pattern of complex action potentials and activity. Other neurotransmitters may be involved in these activities as well. The effects that inputs and outputs have on each other in this system as well as the pattern of action potentials mediated by hallucinogenic drugs help to cause many of the complex changes that allow hallucinations to happen. (B.L. Jacobs, "How Hallucinogenic Drugs Work") Scientists continue to do research to determine the exact effects that hallucinogens have on the serotonin receptors and to answer any questions that they cannot yet answer.


WWW Sources

1) NIDA (National Institution Drug Abuse: LSD(Lysergic Acid Diethylamide).

2) Hallucinogenic Drugs in Psychiatric Research and Treatment: Perspectives and Prospects.

3) Tryptamine Hallucinogens and Consciousness.

4) Hallucinogens (PCP, LSD, etc.).

5) Narcotics, Dangerous Drugs, and Marijuana.

6) Healthguide Online: Substance Abuse: Hallucinogens.

7) Hallucinogens.

8) Los Angeles Police Department Drug Recognition Expert Unit: Hallucinogens.

9) Postulated Mechanisms of LSD.

10) B.L. Jacobs. 1987. How Hallucinogenic Drugs Work. "American Scientist". 75:385-92.

11) M.C. Bindal, S.P. Gupta, and P. Singh. 1983. QSAR Studies on Hallucinogens. "Chemical Reviews". 83:633-49.


Comments made prior to 2007

When you list the drugs in the beginning of your article you list lsd psilocin and mescaline. But "psilocin" is not actually the active ingredient in hallucinogenic mushrooms. The correct term is "Psilocybin". Just thought I'd point that out ... Daniel, 19 February 2007


Anonymous's picture

Do acid. It is not as crazy

Do acid. It is not as crazy as people hype it up to be. You will find it will make you feel very happy and peaceful, and you will have a deeper understanding of things. On just one hit, you will be in control of your body and what you are doing. Hallucinations are very subtle, stuff warps a little if you stare at it, but you can walk around, talk to people, and function very well on just one hit. Its like normal life, amplified.

Anonymous's picture

If you're 15 you shouldn't

If you're 15 you shouldn't be doing any drugs (including drinking). Your brain is still developing and your perceptions of the world hinge on reliable input from your real-life experiences. I've known a lot of people who did all kinds of drugs, and I find that the people who started smoking marijuana in high school have a tendency to be unable to cope with real life in their twenties and, frankly, come off as out of touch and kind of pathetic. LSD is absolutely life-changing, but so is being in high school, your first love, leaving your family to be on your own, going to college, turning 21--you're a long ways away from the point where life is boring and *needs* a change.

It's not like THC or being drunk at all and you might really enjoy it or you might have the most terrifying evening of your life. And since you're in the middle of puberty right now, your hormones are already out of whack, which isn't going to put you in a good position to being with.

cesar aguirre's picture


im 17 years old , and ive been droppin acid for about 4 months now at raves mostly, and im still normal. i drop acid at least 3 times a week sometimes more.
LSD is not dangerous.!



Tho LSD is not dangerous and no one has overdosed on it. it is still very bad for you and could be dangerous if you have a bad trip which could happen to anyone even you so do LSD when your happy NOT sad or you might have a bad trip and could hurt someone or worse your self...

Anonymous's picture


Thats crazy!. Im 17 and I have done acid a few times and definatly my share of mushrooms,weed smoking and others but i mean come on! Is your life that boring that you drop acid 3 times a week. And to think that this has no effect and isnt dangerous is crazy! That shit fucks with your mind and CAN not always but can permantly damage your mental state for life. It has helped alot of people in crazy situations like with OCD, post traumatic stress and even people with terminal cancer but there are also HUNDREDS of cases of people commiting suicide and murder and insane things like that because of LSD.
Now im not some 'straight edge, jesus pushing, annoying anti drug person' im definatly into the stuff but i just think you should do some reading my friend. Just cause your fine right now and feel no effects..the next time could be it and as you age im sure youl see the effects.

All im saying is BE SMART!
good trippin' to all

Anonymous's picture

I think not

LSD being stored in the spine in an urban legend; it has a half life of 3 hours and the body processes it entirely. Anti-drug campaigners(?) made up the spinal myth because it's not easy to verify and sounds like serious business. LSD trips are certainly serious business and I have no doubts that you can really mess with your mind for life if you take it too often, but people need to stop propagating this spinal fluid silliness.

Anonymous's picture

u are all crazy

any of yall that do hallucinogens yalls crazy. i mean u could die frum that stuff so why do u do it?

Anonymous's picture


You could DIE driving to work!!

Why would you put yourself in that kind of danger?

You should just dig a hole in the ground, about 50ft deep, get yourself some food, and cover the hole.

Thats the only way you'll ever be safe.

Oh wait... your still gonna die anyways.

Anonymous's picture

In There For Life

The unique thing about LSD as opposed to pretty much every other drug is that it stays in your body for your entire life. THC can be totally removed from even a chronic smoker in a week if he does the right things. Cocaine is untraceable in your body after 2 to 3 days, depending on metabolism. LSD on the other hand never leaves your body, and can be traced in your spine with a spinal tap after one dies and had used LSD earlier in life. Luckily for all you psychonauts out there, it is extremely difficult and expensive for any job to test for LSD :)

Be careful though.. drugs effect everyone differently. Some of my friends love the drug and are always up to do it... others say its too intense to do often and do it very rarely. A couple of my friends absolutely hated it and never want to do it again. Know what you're getting in to, because it will probably change you for life. Its good to do research like this; LSD is not a drug for anyone that just wants to have a good time, it can be a rollercoaster experience in every aspect.

To the people that commented and said you have vertigo like symptoms after chronic lucky thats all you have. Syd Barrett from Pink Floyd went clinically insane from doing too much LSD. He was committed to a mental institution for the majority of his later life. People say his sentences made no sense when he talked and he habitually brushed his teeth. Also, Jerry Garcia, who its been said had a goal in life to always be tripping, pretty much makes no sense when he talks if you ever watch interviews with him in his later life. I used to work with an older guy at an animal hospital who used to be a major LSD user during the hippie era; he would actually have what he believed were real conversations with all the dogs, he was pretty creepy. I'd take vertigo over that any day.

Anonymous's picture

Trying it once

I want to try it for the first time on my birthday. I was wondering what are the most severe things that could happen because of this. Both short term, and long. I plan on marrying my girlfriend and I don't want this one trip to destroy what I have. It says it alters ones perception after the trip, like your experiencing a new thing you never have, and it has completley changed your life.

M-So's picture

About the birthday thing,

About the birthday thing, all I have to say is find 2-3 good friends that you like to hang with, pick something fun to that you all like to do (play video games or whatever) have some money out so one of your clean friends can get a pizza about 1/2 way through, lastly unplug you internet, lock your doors and all in all keep the outside out. The last think you want is something happening that you did not plan on, that will mess up the hole thing for you.

italianpitbull91's picture

effects of acid on the mind

if anyone knows the medical effects of acid on the brain especially the cerebellum please let me know. i am writing a report for school and i need to know so if theres any health care proffessionals looking through this please respond thanks

Sarah Wilkinson's picture

Reply to 1st LSD trip on your birthday!!

I have done LSD a few times when I was younger (as a teenager) and my advice is that you shouldn't even bother. It is a nasty dirty drug and the way you feel coming down off of it is nasty. If it is any idication as to what it does to your body and brain than that is a scary thought. Stick to simple things like bud, and maybe even shrooms, anr a good alternative. That is just my personal opinion. If you do decide to do it then make sure you are around people you trust to take care of you if something goes wrong cause if you have a bad trip than your stuck dealing with it for like 8 hours.

Man who stumbled on comment's picture

I definitely disagree. I

I definitely disagree. I think that marijuana feels dirtier as the effects feel more sloppy. I would recommend trying it because you can read as much as you want, thousands of reports, but you still wont know what the experience is like. And isnt that what life is all about, living through experience.

Anonymous's picture

Yeah I agree. you can read

Yeah I agree. you can read all you want and ask people all you want but you'll never know until you try it. I seriously doubt doing it once will really affect you very much afterwords. Really. I think everyone should try it just once. And you won't necessarily have a bad comedown either. It varies by person. I didn't have a nasty comedown, i just couldnt sleep but it was fine.

M-So's picture

About the the comedown, I

About the the comedown, I don't know what you took to have it so easy but I tried acid once and it was the 2ed hardest thing I have ever went through in my life. I took it on a Friday and for the next 2 days I was puking unable to eat anything and then Monday was a test that could not be missed, so shacking I stood up and did what needed to be done to get to that test and I passed with %75.

Anonymous's picture

affects of hallucinogens in later years: REPLY

LSD is often trapped in certain cells in the brain/spinal cord having vertigo or flashbacks in later years could very eaisily be caused by these cells breaking down and releasing the drug back into your system

Caseyyy's picture

well basically i've done

well basically i've done acid a few times.. and let me tell you it was amazing.. i havent dropped in awhile but occasionally get awesome flashbacks.. ecspecially when i smoke the herb.

Anonymous's picture


what is the effect that lsd has on the brain
what effect does marijuana,alcohol,heroin,inhalant,nicotine, and steroids have on the brain?
what part of the brain is effected by these drugs?

aub's picture


okay so is it true acid makes your spinal chord bleed?

Anonymous's picture


no not at all does it make your spine bleed

Mark Huerta's picture

affects of hallucinogen in later years

I'm one who abused LSD in my high school years (1973 to 1975) and a little in my adult years. The last use of this drug was once in the latter part of 1976 then last time was once in 1985. The heaviest use was as a 15 to 16 year old teen where it was literally every other day, at 17 maybe three times a month. Now at 50 years old I have a form of vertigo mostly. It’s a continuous internal feeling of dizziness with an occasional feeling of LSD, or the beginning stages of the drug, without the hallucination.

I am going through test with my Doctor but they are not sure, as yet, what’s causing this.
I'm wondering if there any medical knowledge of this being a result of long term abuse later in the life of an abuser?

Anonymous's picture

Acid trips in younger life causing vertigo in later years

If you or anyone believes that vertigo is caused by many acid trips in your younger days, how would one explain the fact that there are people who tripped a lot in their younger years and do not experience vertigo in their later years (probably hundreds of thousands of people over the world).
How also would one explain that there are also many people who experience vertigo that have never touched a drug in their lives.
These two things are not correlated.
Believe what you want.

Anonymous's picture

"If you or anyone believes

"If you or anyone believes that vertigo is caused by many acid trips in your younger days, how would one explain the fact that there are people who tripped a lot in their younger years and do not experience vertigo in their later years (probably hundreds of thousands of people over the world).
How also would one explain that there are also many people who experience vertigo that have never touched a drug in their lives."

I think the way to explain this is that everyone in the world is different.

Anonymous's picture

Mark Huerta

I have heard of your case before, one of my friends did lsd constantly many hits a day and he is in the same state of mind as you.

mike becca's picture

i gotta say, i havent done

i gotta say, i havent done acid near as much as you, im only on my 23rd trip. but i do believe your experiencing vertigo because your brain became slightly accustomed to the drug and now that its gone your body is working to produce a filler for the void where the drug once was. this is only a theory, but i beleive it has some basis to it because the body will produce what it lacks if necesary.. but one can never really know unless you can delve into the mind of another person....

Anonymous's picture

It has nothing to do with

It has nothing to do with your brain. The LSD that you took earlier was stored in your fat cells. When you start to burn those fat cells, you get flashbacks that make it seem like youre on the drug again.

cheech's picture

cool and i dont have to paid

cool and i dont have to paid for that

Anonymous's picture

That's not true. Sure some

That's not true. Sure some may get stored in fat and be released if you're running a marathon, but 20 micrograms that you took several times won't be messing you up for years.

Anonymous's picture


Flashbacks occur even if you have been off the drug for years. As a long time user you may be having diluted flashback episodes and the confusion your body associates with LSD Vertigo and dizziness.

Anonymous's picture

Also; another hallucinogenic

Also; another hallucinogenic is when you chew the stem of a Marajunana leaf. But it also makes you uhh... die.

Anonymous's picture

lmao! you can not die from

lmao! you can not die from marijuana, it is impossible to overdoes.

Serendip Visitor's picture

control subject

Those in this research study who smoked marijuana had their chances of a heart attack increase 4X's more than that of the other group who never smoked marijuana. Marijuana increases the force of the contractions in the heart chambers, you can experience a pounding heart with hash or with hydroponic marijuana smoked in a bong. I know this from smoking potent marijuana myself. So how true is the age old remark that it's harmless because you supposedly cannot suffer a fatal overdose? It's not all that true. Your chance of a heart attack are greater while smoking marijuana. Driving or operating machinery can result in fatal accidents if you have smoked marijuana before taking a go at it, which needless to say would be very stupid. One day the neighborhood weed dealer is going to tell you that they can get any drug you want, it want be easy for you to take a stand, you're already getting high!it's very common,all of that happened to me and I tried another drug a harder one. Some of us shot up heroin after a while. I'm drug free. I'm afraid that drugs unleash the worst in me every time, I can become quite a kook. I 'll remain sensible and not go all cuckoo. I hope that you understand this later.

Anonymous's picture


that is not true because you cant over dose on weed

Anonymous's picture



I am not really a chronic drug user, although I have done my share of mushrooms, marijuana, and I dropped two hits of LSD on October 25th, 2008. I had always wanted to try LSD, but wasn't sure because earlier in September of 2008 I did an eighth of mushrooms, had an AWESOME trip, and ended up having a bad trip, so I was somewhat reluctant to try any other hallucinogens. I did some research and a section from the above, highlighted article from Wikipedia entitled "Bicycle Day" solely led me to drop the two hits. I also researched LSD on the second website, The Vaults of Erowid, which encompasses nearly all known drugs, their basics, effects, doses, etc. It was the best experience of my life and I'm glad I experimented with it. Every person's experience with drugs varies; however, when in a stable state of mind (meaning no distractions or undertakings you need to pursue/accomplish, i.e. homework, meetings, employment, etc.), people you want to trip with and trust tripping with (or maybe if you trip by yourself like I did), listening to some of your favorite tunes (Incubus, Bob Marley, etc.), and being somewhere you WANT to trip (i.e. nature, familiar areas like your house/room) then you're experience may be exceptional. Once again, this is not for everyone, but if you do decide to experiment, hopefully the above websites can be of some assistance.

Anonymous's picture

I used to grow and smoke

I used to grow and smoke all the time. I've made food products from pot. Sometimes taking out the THC. Sometimes just throwing the weed right in to the mix and we were not picky. Buds, seeds, and STEMS. You can not die from chewing on the stem. Infact, the seeds are a better protein than all meats and nuts. Oh, and I used to chew on the stems all the time and I never hallucinated.

pantalones's picture

not true

I smoke marijuana all the time and always chew the stems, I guess you can choke on it and die, but marijuana has no poisoneus(sp) chemicals in it.

Anonymous's picture

well... technically

The actual chemical reaction of THC is considered posionious...

Then again, I still smoke about an ounce a week. I just enjoy the pain ;)

Anonymous's picture


how and what do you mean by technically

Anonymous's picture


my b/f chews the stem of the marajunana leaf and he is not dead so that is not true.

Serendip Visitor's picture


According to Carlos Castaneda, taking a hallucogen makes your 'focus' point shift - the point that helps you make sense of everything around you and to keep you 'sane'. The problem with taking the drug without an experienced person to help you means that your focus point can go anywhere, even to a lower, animal realm of perception. Thus, you can feel incredible surges of energy and a greater understanding and feel for the natural world.
We need to be able to make sense of our world, but constant taking of, for instance, LSD, can make your focus point shift permanently and thus render you 'insane', 'schizophrenic', etc. much as in the case of Syd Barrett, who was halfway there already!
Taking a hallucogen, I believe, can be very beneficial in opening up your spiritual nature and giving you a greater, innate, understanding of what is around you, but, and it's a big BUT, it should be done very sparingly and with people who know how to help you if you have a negative reaction or experience.
Everything should be done for the purpose that it was intended for. Things exist for a reason, so use them for that reason, and not simply for 'getting out if it'. This is the great problem with drugs in general - so many people see them as just recreational or as a means of blotting out the bad things in their lives.