Why Do Some Drugs Make Your Pupils Wider?

Why Do Some Drugs Make Your Pupils Wider?

[ ♪ Intro ] Whether or not eyes are the windows to the soul, scientifically, pupils are the windows of the eyes. And sometimes those windows are more open than usual, like when you’ve taken a medication that causes pupil dilation. Or when people use certain recreational drugs. It all comes down to how different chemicals can cause changes throughout your whole body, which can affect little muscles in your eyes. The pupils are openings that let light into
the rest of your eye. And the colored part of your eye, the iris,
controls how much light makes it in. The balance of two muscle groups in the iris changes how big your pupils are, like a camera aperture. The iris dilator is arranged like bicycle
spokes around the center of your eye. And when it contracts, it pulls your pupils open wider. The iris sphincter, on the other hand, is in a ring around your pupil that acts like most of the sphincter muscles in your body. It constricts your pupils down to little dots. So now you know that you’ve got a sphincter in your eye. That’s just a fact for you. Anything that blocks or stimulates either muscle can knock that balance out of whack and cause some really noticeable changes. For example, drugs that block receptors for the neurotransmitter acetylcholine can cause impressive dilation. These medications are designed to inhibit
the parasympathetic nervous system, which controls the involuntary muscle contractions that keep things moving in your body, like your lungs, or the plumbing that gets rid of waste. This system also controls the iris sphincter muscle. So when it’s inhibited, the iris sphincter can’t counteract the pull from the iris dilator, and you get wide open, “blown out” pupils. Some drugs, like ones for overactive bladders or excessive sweating, target the entire parasympathetic nervous system. They often have dilated pupils or blurry vision as side effects, but those aren’t the goal. Others, like the drops used to dilate pupils for eye exams, are more targeted and don’t throw your whole body off. Now, other drugs can stimulate the sympathetic nervous system, responsible for your body’s fight or flight response. And these too can cause dilation. Take adrenaline, which floods your bloodstream when you’re scared but is also a medication for extreme allergic reactions—it’s what’s in the EpiPen. Adrenaline can bind to nerve receptors connected to the iris dilator, making it contract and pull your pupils open wide. If people use drugs like cocaine, amphetamines, or even weed, their brains have more dopamine and norepinephrine floating around. Usually, either extra neurotransmitters get released or receptors that naturally suck them away get blocked by those drugs. These chemicals are involved in the “high” feeling but also cause dilated pupils. Scientists think that dopamine makes certain nerve cells release more norepinephrine, which works like adrenaline to make the iris dilator contract. So wide pupils can be caused by a lot of things. But they’re a hint that certain chemicals, illicit or not, are bubbling through your body. Thanks to our Patreon patrons for asking us great questions like this! If you want to support us and send us questions, and get some other cool stuff you can go to patreon.com/scishow. And if you want to learn more about human eyes, check out our video where I explain what those pesky little eye floaters actually are. [ ♪ Outro ]

100 Replies to “Why Do Some Drugs Make Your Pupils Wider?”

  1. Dilation from non natural causes is termed "eclipsed" For example, My cat ate all my dextromethorphan and if he does not die, his eyes will be eclipsed for a week.

  2. I was gonna point out that dopamine is also the same endorphin that activates when love is felt so that’s pretty cool

  3. When I was briefly on SSRIs, my pupils dilated all day. Thinking back on it I assumed there were serotonin receptors in the muscle, but I guess it might have been a secondary effect.

  4. i knew it was the adrenaline. fight or flight – might need that extra light. yeah i just came up with this.

  5. I have epilepsy and my pupils get the idea that they should begin to constantly switch between bigger and smaller at times. And (luckily a little more rarely) sometimes they have difficulty keeping focus on the correct distance and I get a tunnel vision. It's quite annoying sometimes. :/

  6. I think serotonin plays a much bigger role in this than dopamine and norepinephrine. I am prescribed Ritalin, which is a dopamine, norepinephrine, and noradrenaline reuptake inhibitor and Citalopram, which is a selective serotonin reuptake inhibitor. The Ritalin doesn't cause any pupil dilation, but the Citalopram does.
    Also, the classical psychedelics like LSD and Psilocin interact very selectively with the serotonergic system and cause very strong pupil dilation.

    How does this make sense?

  7. Could we please get an answer to how stones get in my shoe!!! Even when I'm wearing laced up boots it gets in 😡. If initially the stone moves because I step on it and it flicks backward, how does it somehow gravitate back towards my shoe and get inside. Any logical answer would be much appreciated 😁

  8. Good video, however im not sure that dopamine is related to pupil dilation, specifically opiates cause pupils to constrict to tiny pinholes, and are some of the most dopamine releasing drugs. Anecdotally I have not seen dilated pupils associated with marijuana, but if pupils were to dilate I would argue that marijuana or other substances only promote wider eyes, in comparison to something like mdma or traditional hallucinogens which make my eyes look more dramatic than what google shows for "dilated pupils" :^)

  9. Fun fact: Some people have learned to control the muscles in their eyes that dilate their pupils, and can dilate their pupils voluntarily. It's a useful technique for free-divers to allow them to see better underwater, given that their limited air-time makes their eyes' normal dilation period insufficient.

    Video demo here: https://www.youtube.com/watch?v=ELvjHZhhFEg

  10. Sorry, Hank but EpiPens DO NOT contain Adrenaline, they contain EPINEPHRINE. Your researchers goofed on this one!

  11. Often, when I took a certain drug, I've one pupil contracted and the other dilated; very strange and people have issues watching me in the eyes when that happens. o_O

  12. Hank, give some of us a little credit. I've read An Abundance of Katherines, I know what a pupillary sphincter is.

  13. Under normal circumstances with pupils dilating due to light conditions they'd want to keep a fixed level of light coming through. If they were to dilate whilst the light didn't change then why would you not perceive things as brighter?

  14. I want to know. How does a snail possibly "sleep" for years, can they even like kinda shut themselves off for like years?

    How do they breathe under the shell if they do like "hibernate"?

  15. This kind of gives meaning to the line, "my eyes become enlarged
    And the light that you shine can be seen."

    Lyrics to songs can sometimes start to make sense when there is a bit of context. It's probably a coincidence that I watched Batman Forever last night and started wondering about the formerly nonsensical lyrics to it's theme song. It all makes sense now. Snow must be a euphemism for cocaine. That is actually a well crafted song in context.

    The only thing that doesn't is why someone decided a totally irrelevant song needed to be the theme song. That doesn't much matter when the whole plot of the movie is equally nonsensical.


  17. Hvad er ideen med at tale så hurtigt ? Har det en mission, er det en amerikansk opfattelse af, at hvis man taler hurtigt og uden at trække vejret, så er man mere troværdig (amerikanske reklamer tyder på at det tilsyneladende virker). For en europæer virker det mere som afliren af en indstuderet tekst/ide, end som faktuel viden.

  18. Me and some members of my family have a rare mutation where our pupils are very dilated most of the time, except when there's lots of light. It freaks some people I meet out when they see it because drugs.

  19. Why were "Stormy" Daniels' pupils so dilated (open), during her recent interview on 60 Minutes? Correspondent Anderson Cooper's pupils were normal; i.e., very different from the interviewee. They were subjected to the same stage lighting conditions. Ms. Daniels eyes were inordinately open to light input, and that was very noticeable to me.

  20. Just cause people have heard of the anal sphincter more often than any other doesnt mean its the only one or that its somehow weird. Saying it that way will help enforce the poo bias in science.

  21. THANK YOU SCISHOW!!!!!!!!! But WILL YOU PLEASE DO A VIDEO ON GLIOMAS??? Or at least give me a yes or no????

  22. *No dumbass the corneas are the windows of the eyes. Doin' pretty bad right out the gate kid. Furthermore a pupil is like a hallway entrance directly in front of that window, but without a door.*

  23. Just got the signed script of this video from my P4A perk! Love it so much, and love the video! Thanks Scishow!

  24. youre in a dark room
    the fbi bust through the door
    "you are under arrest for use of illicit drugs"
    ahh piss

  25. My eye pupils are also dilated. I don't know reason behind it. I don't use any drugs . Plz tell me some remedy 😢😢😧😧😧😕😕😕😕

  26. I stay seeing you all the time and I don't even know who you are. I've asked enough how and why's that I've gotten to the point where I see you often so you've definitely earned my like and subscription

  27. I feel like I can do anything right now, I woke up with my pupils so huge right now…

    Everything looks so weirddd

  28. I wouldn't through cannabis in the mix with cocaine and amphetamines as a substance that causes pupil dilation. More often then not, cannabis users experience constricted pupils instead. This occurrence can be seen in substances like opioids and benzodiazepines as well

  29. Could u please make a video with slow, clearer speech, considerate of some stressed ppl whom this is new to, and help us understand? Thsi is activating sympathetci nervous system more and it's hard to get what u re saying.

  30. What r those eye floaters?… I always ask myself that. Like almost transparent but not exactly. Like when I move my eyes left n right I can kinda see these things that seem 2 be floating or w.e.

  31. I was wondering this person gave me something that looked like meth and I started seeing different color light I would think it was cops at first but when I started seeing green purple orange I was sure I was not on meth I went to the hospital that night and I couldn’t open my eyes the person who gave this to me was suppose to be my friend

  32. Lmao my pupils are so big but its just that i ws to eye doctor and she put some eye drops or DID SHE 😱

  33. My mother thinks I’m doing crack because my pupils are always huge.
    When my eyes are wide open and I have huge pupils, I’m on crack, when my eyes are barely open and I have huge pupils, I’m depressed,
    According to my mother.
    So basically, I can’t have a straight face without looking like a depressed crack head.

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