I’ve taken hydroxychloriquine for an auto-immune disease I have and I had an adverse reaction (blistering rash!).
It could be the sulphur component. I even have to check the alcohol for sulfides. Drank a hard cider in England and started a rash immediately. Then saw the label. Ugh.
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I’m really not sure about the sulfa. I have taken sulphas years ago before the AI reared its ugly head and don’t remember a problem. I have also taken Methotrexate and you aren’t supposed to mix sulpha with that so sulpha is a no-no on my medical records.
You can also develop a drug allergy at any point. My adverse reactions actually started after giving birth to my first child. I already had other drug allergies so not surprising this one started. But it started after I had taken it before with no issues.