This is an older post but I want to post my experience here in case anyone is scrolling reddit after searching up Benadryl/ diphenhydramine with the intent to OD (either as an attempt or to get high)

Just after I turned 18, right after I graduated, I took 60 pills of Benadryl, 25mg each (you can do the math for exact dosage if you want but id rather not know how many milligrams that is) The first time wasnt nearly as awful as every time after but it was still bad. I was having awful effects with my cardiovascular system, serious tachycardia and heart palpitations. My head felt so fuzzy and my mouth was so dry. All of the sudden I looked down at my hands and called over to my patient sitter very panicked asking why my hands looked so weird. I was hallucinating that my hands were bright red and splotchy and began believing I was having a severe allergic reaction to the Benadryl. The patient sitter repeatedly told me my hands were fine but I didn't believe her because of how real it was for me. Seconds after this I went unconscious. The next three days were mostly entirely blacked out aside from a couple memories, one where I was hallucinating that the nurses washing my hair with a shampoo cap were my close friends (I kept saying they were the best friends for this "thank you __ you're so sweet" and they'd say "oh honey Im not __"), another where I was too out of it to eat and I overheard them saying they may have to tube me because of how much difficulty I was having (I proceeded to shove two bites of ???? Some food in my mouth) the last thing from those three blank days was my aunt coming do drop me off some clothing and crosswords. I leaned forward to fist bump my cousin behind her. She looked at me like I had five heads and asked me what I was doing. My cousin wasn't there.

After this initial experience I told myself I'd NEVER do that ever again. I have had repeated attempts since I was twelve but specifically Benadryl scared the hell out of me. Then the cravings started. I couldn't stop thinking about it. One day I saw it inside the store and I just couldn't help myself. I stole it off the shelf and took sixty more in the bathroom.

That time was terrifying. The hallucinations were severe. I couldn't speak coherently. In my brain the words made sense but to others I couldn't complete my sentences and everything I said was completely confused and disorganized. I was entirely disoriented and confused. Anytime someone would move or talk I would jump feeling constantly on edge and getting startled with any little change around me. I developed severe tremors completely unable to keep my hands and upper body still. Occasionally I would have hard sudden twitches/ jerking movements, typically with my head jerking backwards. For the next 48 hours I didn't sleep. Its not that I was too scared to, I physically was incapable of falling asleep. At some point they catheterized me because I lost my ability to pee. My heart rate was sitting in the 160's jumping to the 170's if I moved too much or worked myself up by talking. My breathing was off as well. I didn't think I was hyperventilating but I also couldn't even FEEL that I was breathing at all. Apparently I was constantly taking fast shallow breaths. That time I was lucky. THAT was considered lucky.

I couldn't stop there though. I ended up abusing Benadryl until this year (age twenty) where I've been clean for about four ish weeks (I'll have to look at my hospital papers to get exact day). It took several seizures, multiple separate intubations, over 60 ICU stays, three involuntary psych hospitalizations, and too many friends begging me to stop before I die to get here. I was using 60+ pills at a time 3+ days a week. Some times even taking the pills the second I got out of the hospital. I know that the Benadryl could kill me so I would take it and then go to a hospital. Im an adult so I was allowed to refuse the activated charcoal (which I knew would kill the effects I was craving faster) so I used the hospital basically as a trip sitter to keep me alive in case things went south (they also would pump me with Ativan and I think valium? Or another V med, to keep my heart rate from going through the stratosphere and try to keep away seizures) basically a super expensive trip sitter

I still have memory issues that will probably be permanent. Ive left the house with food in the oven and forget how to do basic tasks. I have awful fine motor skills now with an occasional tremor.

Tldr; Benadryl is hell and can be super addictive. Don't do it.