I became VERY irritable when I started pain meds 10 yrs ago. I already had anger probs, but had a longer fuse. I wasn't ALWAYS angry or anything. But when I started pain meds I had a shorter fuse and things irritated me more than they used to. Smaller, less significant things, too. And I seemed to get more upset and my reaction was more uncontrolled. I went to the psychiatrist and was diagnosed as bipolar and put on mood stabilizing meds, which have helped. But other "sane" ppl I know and have talked to about this mentioned the same irritability. I did feel pretty angry all the time, but I also have kidney failure and do dialysis and was going thru a hard time, and my close family member was abusing drugs in my house and I was VERY angry about that, so it was exacerbated.
But I remember after my kidney transplant in 02 when they gave me percocet, first time taking pain meds, I got irritable then, too. And my husband a BFF also get irritable on pain meds. It's directly related to the meds, too.
Some other things I noticed when starting pain mess, aside from EXTREME constipation, were feeling afraid at night. I'd have nightmares and just have a feeling of fear and terror when sleeping alone or being alone at night. I saw that in my mom when she started pain meds as well. That went away tho.
Also, I became VERY chatty, and would speak my mind more, not always a good thing. I wouldn't take others feelings or privacy into consideration very often. The meds make me not really think before I speak, and this has NOT gone away. I try to do better, but ppl have come to know me this way, unfortunately. Like my 16 yr old niece doesn't really remember me non-"bossy" or irritable. But the psych meds have helped. Hope this helps.