I'm currently in Afghanistan, and we take doxy every day. We have had several cases within our unit, always of guys who blew off the daily pill. I was in Haiti many years ago and took Larium. The dreams (and hallucinations for those who would intentionally take too many) were pretty unreal.
The Army is pretty active on preventative treatment. With the doxy, we are warned to keep taking it several weeks after redeployment. Apparently it only counters the parasite in the blood. The liver can retain them for a certain period of time.