How long does it take to experience the side effects of doryx (doxycycline)?

Hours to days to ...: Doryx (doxycycline) is a slow-release form of doxycyline, a tetracycline-type antibiotic. Common side effects include headache, nausea, acid stomach, joint pain, diarrhea, rash, yeast infections, menstrual cramps, skin discoloration, abnl kidney test. More serious side effects are also possible. The common side effects may start with the first dose; most will occur later; some can occur after months of use.