This was originally written after my trip to India in 2001. It's still valid in 2006. I took Doxycycline again on my six month Asia trip, with almost no side effects.
When you're going to India, most medical authorities recommend that you take anti-malarial drugs. There are several options available, but the two most commonly recommended are Lariam and the more recent Malarone. Roxanne and I chose another option, Doxycycline. Catherine also chose another alternative, Chloroquine (this is rarely recommended anymore as there are resistant strains of malaria). Farley (one of the two trip leaders) has been travelling to India for years, and he never takes anti-malarials. If you think about it, the whole population of India (all one billion of them) aren't taking anti-malarials, so this is also an option. Whatever you take, you'll be required to take it for at least four weeks after you return, as malaria can lie dormant for that long.
"What? I thought you were taking an anti-malarial. Doesn't that prevent you from getting malaria?" No. It slows the disease's reproduction in your bloodstream enough to either kill it or allow you the time to get to a hospital before the malaria gets into full swing. Unchecked, malaria acts fast: you can go from first signs to immobilized in about two days, and you may be dead five days after that.
Lariam is probably the commonest anti-malarial right now. Its best known side effect (and we definitely saw this on the trip) is "vivid dreams." It's a weekly pill, and the day after everyone took their Lariam, we had some very interesting reports of dreams. Some were screaming nightmares, one or two were actually reported to be rather nice (but that seems to be the exception).
Malarone is a relative of Lariam, but it's a daily and the side effects aren't as pronounced. Its biggest problem is price: it costs four or five times as much as Lariam for the same time period.
Doxycycline is a broad spectrum anti-biotic. It's "90% as effective" at stopping malaria as Lariam or Malarone. The big added plus of taking doxycycline is that it will kill nearly any bacteria that you could catch from the food and the water, so Roxanne and I were among the few who were never knocked out of circulation by diarrhea and/or vomiting. The down-side of that is that it messes with your stomach anyway, because it kills off all the beneficial bacteria that normally live in your stomach as well as the bad ones, and my digestion remained messed up for several weeks.