Clarithromycin
"Only been taking this antibiotic for pleurisy and a sinus infection for 3 days. Day 1 bad bitter taste in mouth and terrible thirst. Day 2 diarrhea. Day 3 the worst headache I have ever had. This drug should come with a GIANT warning on the packet. DON'T take this drug it has vile side effects. My Dr has told me to stop it immediately.  So I have!"