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Old 12-30-2017, 12:25 AM
Join Date: Dec 2017
Posts: 25
Why does diphenhydramine hcl (Benadryl) cause 'worm and spider' hallucinations in many people?

Just came to the U.S. a few days ago for a trip and stocked up on bargains for antihistamimes which I can't find anywhere else in my country.

I wanted to take a lot (not recreationally but for sleeping) but then I rememeber reading on a drug harm reduction forum as well as reading experiences on Erowid that large doses will cause extremely unpleasant or frightening hallucinations. These range from seeing worms on your skin, spiders on the ceiling, dizziness,

What's the cause for this scientifically? Are there specific parts of the brain this drug acts on to produce bad hallucinations instead of 'good' ones like mushrooms and LSD?
Old 12-30-2017, 12:49 AM
Join Date: Jan 2010
Posts: 6,282
It's an anticholinergic which inhibits the parasympathetic nervous system. The PNS brings your body down and handles things like rest and digest. The sympathetic nervous system brings your body up and handles things like fight or flight. The SNS and PNS are in dynamic equilibrium so inhibiting the PNS should result in increased SNS activity. This means that at high doses, Benadryl may in some ways act like a stimulant. Overuse of stimulants can result in stimulant psychosis:

I don't have any first-hand experience with stimulant psychosis but I understand that having creepy critters crawling under your skin is typical of stimulant psychosis.

As for why they would tend to be bad hallucinations: If you let the SNS run wild, your fight or flight response will go through the roof, hence your delusions will tend to be negative and related to threats. Also note how people on crack or meth often pick at their skin; There seems to be something about high doses of stimulants that makes people be hypersensitive, obsessed and irritated with their skin. Mix that with a propensity for delusion and increased threat perception and you have an Indiana Jones crypt under your skin.

Classical psychedelics like LSD are chiefly serotonergic which tends to improve mood.

Last edited by MichaelEmouse; 12-30-2017 at 12:52 AM.
Old 12-30-2017, 02:03 AM
Join Date: Nov 2017
Location: Fenario
Posts: 1,805
I can personally attest to having, many times, hallucinated a spider on the ceiling in the very earliest moments, like a few seconds, after waking up from sleep. It's always the same, it is kind of blurry, like a child's scribble; is large, like the scale of a tarantula, and has many more legs than an actual spider would have, and it makes a jittery, shaky motion as it gradually fades away. As I said, it lasts for about three or four seconds, beginning immediately after waking up and opening my eyes. It's happened many times. Diphenhydramine wasn't involved, though.

I have also had extremely intense, half-asleep/half-awake, dreamlike adventures on Nyquil or other medicines containing dextromethorphan. I'm not even talking drinking a whole bottle like some people do, just an extra capful or so above the normal dose. Crazy, crazy experiences, during which it's exceptionally difficult to judge whether I'm awake or asleep.
Meet me at Jacquernagy Park.

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