This sounds like it could be a multifactorial problem. Since there is likely nothing the patient can do, the rest is somewhat up to the situational approach, which is usually always communication, which youve already likely finely tuned.
You mentioned “wanting to know what is wrong”, but I am wondering how you go about wanting to learn what leads people to reach their conclusions. It’s certainly an art and takes practice and some skill building and some reading:
Motivational interviewing for healthcare professions,
Book: Art of Positive Communication https://www.amazon.com/Art-Positive-Communication-Theory-Practice/dp/1433120992
Book: How We Know What Isnt So-The Fallibility of Human Reason in Everyday Life by Thomas Gilovich
4: EdX course: The Science of Everyday Thinking.
3 and 4 here are shared here to get a broad sense for how people come to their own conclusions based on cognitive shortcuts that we’re all subject to. Perhaps knowing these can lead us to ask better questions and differently as we seek to fully understand.
I wonder about the interaction between you and your patient that you shared:
Patient: “you gave me Cushing’s because of the inhaler you prescribed me!”
You: “You’re upset because you feel that I caused you to get Cushing’s disease”
Patient: “Yeah! I am not going to take anything else that you prescribe me. I dont want to get that sick again!”
You: “You’re not going to take anything else that I might prescribe you because you don’t want to get sick.”
Patient: “yeah!”
You: “What is leading you to feel like the inhaler caused you to get Cushing’s disease”
Patient: “I was talking to my neighbor whose mother got sick because she was on a lot of steroids and the doctor said she got Cushings and now I feel like I have it and my neighbor told me the steroids from my inhaler can cause Cushings”
You: “I see. I understand a bit better now. Would it be okay if I talked about steroids and Cushing disease and the medications your on?”
Patient: “…….fine”
You = teach.
If patient says no, you could continue asking what the barrier might be, but this has to be balanced so as to not confront the patient enough to drive them away but gently confronting enough to maintain rapport and trust and for them to re-think their stance and to perhaps talk about later, which you or they could bring up. For a CYA moment you could document they refused education and that you gave them a appropriately tailored education material about their medications and side effects.