Eh one every now and then is fine, I take it for motion sickness when going on long car rides. Half a pill is enough. Then again, taking enough to get nightshade-like poisoning is really not recommended.
Long term use has now been linked to neurological issues, it crosses the blood brain barrier. However, yes occasional use is relatively safe. But it is not recommended as a daily antihistamine at all these days.
Oh yes, I’m completely aware. I’m a pharmacist with allergies. I always try to talk my patients out of first-gen antihistamines. Bilastine is my go to these days for myself. Zyrtec and generics as OTCs.
Maybe if you try to trip by taking 100+mg, or use it every single night for a period of decades, sure. If you have a chronic sleep problem you should talk to a doctor, like any chronic issues, before using OTC drugs for any extended length of time. But for short term use you're just spreading misinformation. Cite your sources or don't do that.
It's more of a placebo than an actual sleep aid. It's not harmful though. If you want to take it, don't worry. If you think it helps, then in some small way it does.
But if you NEED to fall asleep in the next hour 25-50mg of diphenhydramine, 1-2 normal Benadryl or Advil/Tylenol/Motrin PM(with they're active ingredients) does a pretty reliable job if you let it. You have to get in bed and give it a shot at working but I find little failure with it. You will however be somewhat groggy in the morning, drink water.
It’s most useful to take 2-3 hours before bed to reset your circadian rhythm. Essentially it mimics the melatonin you make at sun down to prepare your body for sleep. You only need 1-2 mg to do this.
I even think 1 mg is too much. It's active in microgram doses. Also read the Wikipedia page, it's poorly regulated and pills can contain upwards of 4x what they say.