lyme disease
"I've been on doxycycline for about a week now for a bout of Lyme disease and other than some moderate to severe drowsiness (which may be - and is - part of the disease, but does get more severe when I take the antibiotic), and being absolutely unable to take it on an empty stomach (to do so results in nausea and, worse case, vomiting), I have to say I'm feeling much better quite quickly.  If taken with food, I have no side-effects whatsoever.  One of the best and most mild antibiotics I've had to take."