my uncle died 3 days ago, he had had a mild stroke and doctor prescribrd him the pain killers. next day, we found him in his room unconscious. We called 911 and had an ambulance come.
It was said that he had some sort of infection and had a lot of painkillers in his system. The doctor was suspicious as to whether my uncle had ever had a stroke. he died because he was inappropriately prescribed the pain medication, are there legal actions we can take?

You may have legal recourse, but fully assess the situation with more info.
if the druds were purchased on the street and whether the person who prescribed the drug knew of your uncle's past problems etc. so, collect all of the evidence you can, and consult a lawyer.