I have spent months on Doxy (100mg daily) as an anti-malarial. It is a drug recommended for pilots and divers in drug resistant malarial zones.
I realise you are probably not taking the Doxy for anti-malarial purposes but I have also spent a few months on Larium/Mefloquine (when not flying) and can see why pilots should not take it! Everyone I know who was taking Larium suffered side affects to a greater or lesser degree but which were cumulative over time. The side affects were exciting but surreal nightmares/dreams, sleeping badly, behaving in a paranoid and frankly mad way and having very poor memory. I do not plan to ever take it again.
The photosensitivity with Doxy does not prevent you getting a tan but you will burn more easily - so be careful (a bit like being a Scot!).