Doxycycline

Doxycycline is an antibiotic used for both its antibacterial as well as its anti-inflammatory properties. For acne and rosacea it is common for this medication to be used continuously for many months and even years.

Take with food, preferably immediately before eating. This insures that the pill is diluted by food so that it does not irritate your stomach, and that the pill gets all the way down into your stomach. Sometimes when it is taken with a small swallow of liquid the pill will lodge in the esophagus, where it is very irritating, and can cause chest pain.
Do not take Doxycycline immediately before going to bed. While you are lying down the pill can reflux back up into the esophagus, where it can irritate or even ulcerate the lining of the esophagus. Take it at least 1 hour before bedtime.
You do NOT have to avoid milk products when taking this medication. Milk, and anything with calcium or iron, will slightly decrease absorption, but not enough to affect your treatment significantly. (This differs from the older drug tetracycline.) If you take antacids, laxatives, calcium or iron supplements, try to avoid taking these within 2 hours of doxycycline.
Take the medicine regularly. Do NOT stop it as soon as your pimples go away. Doxycycline PREVENTS pimples; it does not really make existing ones go away very well. If you take the medication only on days when you have pimples, it will NOT work, and the acne bacterium is more likely to become resistant to doxycycline.
Doxycycline should not be taken if you are pregnant or breast feeding. If you think you might be pregnant, stop taking doxycycline immediately and contact our office.
Birth control pills: If you are taking birth control pills, there is a small chance that it could keep them from working as a contraceptive.
Avoid prolonged sun exposure, and use a broad-spectrum sunscreen if sun exposure is likely.

Common side effects of Doxycycline

Nausea (especially if you take it without food!)
Vaginal yeast infections -- eating yoghurt or taking acidophilus reduces the chance of this
Diarrhea
Increased sensitivity to sunlight and tanning beds; can sunburn more easily (incidence < 5%, dose-related)
Chest pain (if the pill does not reach the stomach, or if taken immediately before going to bed)

Rare side effects of Doxycycline

Headache
Dizziness

Extremely rare complications of Doxycycline

As with any medicine, there can be very rare, serious reactions, like allergic reactions, liver inflammation, blood cell abnormalities or severe rash. More recently, there have been published concerns that chronic use of doxycycline (and other antibiotics) might increase the risk of inflammatory bowel disease; this is a contested notion, and there may be years before conclusive evidence one way or the other.

References

Epstein, M. E., M. Amodio-Groton, and N. S. Sadick. 1997. Antimicrobial agents for the dermatologist. II. Macrolides, fluoroquinolones, rifamycins, tetracyclines, trimethoprim-sulfamethoxazole, and clindamycin. J. Am. Acad. Dermatol. 37:365.
Maibach, H. 1991. Second-generation tetracyclines, a dermatologic overview: Clincial uses and pharmacology. Cutis 48:411.