What kind of medicine is this? Makes them appear to be always sleeping

My grandpa is an old and sickly person. They recently gave him a medicine that would prevent him from feeling pain but he always looks like he's sleeping and sometimes he moves his mouth likes he's speaking and sometimes does speak

Any strong narcotic can do that: fentanyl, oxycodone, methadone, morphine, oxymorphone/dilaudid, etc...even a mild one can do that to an elderly person or someone with compromised liver function.