What’s the worst reaction you ever have had consuming food, vaccine, medicine and or a drug?

I got dizzy, had a headache, was nauseated, vomited every single day, was constipated for a full week, and began to loathe the idea of eating.
It was a GLP-1, and my endocrinologist still urged me to take it.
I refused. I never got the good side effect of losing weight, probably would have once I started loathing food, but starvation is not my idea of healthy.