Where can I find the best source of information regarding drug interactions?

My Mother, who's 92-years-old, has severe osteoarthritis and has recently started to develop anxiety, depression and irritability. Which realistically, I don’t think she will be able to come off at this stage. I would not be surprised if she is going through onset of dementia as well. I want to give her CBD oil because I have read it that it may be helpful. Where is the best source of information regarding drug interactions? I am already administering CBD balm to her primary source of pain, her knee. Thanks in advance 🙏