It is not commonly understood that medications have different effects when older people are the patients as opposed to younger people.
As we age, medications are often retained in the body for a longer period of time than when we were younger. The consequence is that if medications are not carefully prescribed and administered, there can be a buildup of medications which can have dangerous consequences for the person taking them.
Also, beware that painkillers themselves (opioids such as OxyContin in particular) can cause significant side effects such as balance problems which are more pronounced among older people because such things as balance are adversely affected as a person gets older independently of any drug intake.
In fact, the American Geriatric Society has published a list of drugs which people over the age of 65 should usually avoid. It’s called the Beers Criteria. Listed are such popular medications as Valium, Zanax and Ambien. Google “the Beers Criteria” for a full list.