Health - VERY Scared About Diphenhydramine Use

[mogwai]

A close friend of mine uses Diphenhydramine recreationally. He has told me that he first tried it just a little bit over a year ago, and only used it on a few occasions..

However.. Roughly a year ago he began to use it much more often... As in, every night.. So my friend has been using it every night (minus about days throughout the year) for a year, at about 350-450mg per night.

My friend, who is now 20 years old, is still keeping up their habit, but is becoming worried about their use. They came to me and asked me some stuff, but I really don't have the answers, but maybe some of you can help?

After using it so much, is it very likely that my friend has caused any permanent damage to their body, and is it likely that it will be of significant concern in the sense that it may endanger their life?

My friend is very stubborn, I'm sure he'd admit.. And while it's somewhat unclear how physically addictive this stuff can be, he'd be the first to tell you he's very addicted mentally, which as we all likely can agree on, can be significant enough to get in the way of them stopping their use.

I'm positive my friend wants me to return with news that it's not as dangerous as they might have worried it is, and that they would be okay in continuing their use.. But I don't personally expect that to be the case, and I know my friend has horrible "will power", and wont give up the habit without a fight. Can anybody give me some advice that I could pass on to help? Because... Like I said.. TERRIBLE will power, and I believe my friend is madly in love with this substance.

Thankyou