If a young female in her early 30s dies in her sleep at home, is a test automatically done to see if drugs and/or alcohol played a role?

Both my BIL and his adopted son( sisters son by 1st marriage) died in their sleep. An autopsy said both died of heart failure. No drugs involved.
Strangely, both died in the same house and same bed about 19 months apart. Sister was not present in the house. She was and still is in a nursing home with ALS. She could not attend the son's funeral because of her condition.

I concur with the other answers. It may vary by state law, but in Connecticut, if there is no obvious cause of death, the coroner must do an autopsy to determine cause of death. Even in the case of an accident. (My husband’s niece just died in a car accident last week, no witnesses, one car accident, no sign of a cause. They had to do an autopsy to determine if it was heart related, seizure, drugs, etc.) The coroner must determine cause of death so he knows what to put on death certificate. Can’t just put “died in sleep.”

My daughter a veterinarian had to deal with this exact situation. One of her techs lived in an apartment at the clinic and was found dead in bed one morning. Naturally Police and EMS and coroner had to be called. I did not hear that any testing was done on site but an autopsy had to be done. Everyone was very upset because it looked like a suicide. The results of the autopsy revealed a heart condition that could have killed her anytime which was a great relief to her family and friends.

Don't know but I doubt it. Unless the death was expected there would most certainly be a thorough autopsy done because such an event would be extremely unusual; and no doubt there would be forensic records kept of the site in addition.

Why do you ask?