Do not use tetracycline if you are pregnant. It could cause harm to the unborn baby. Do not take this medication without telling your doctor if you are breast-feeding a baby.

Tetracycline can make birth control pills less effective.

Do not use this medication if you are allergic to tetracycline, or to similar medicines such as demeclocycline (Declomycin), doxycycline (Adoxa, Doryx, Oracea, Vibramycin), or minocycline (Dynacin, Minocin, Solodyn, Vectrin). Before taking tetracycline, tell your doctor if you have liver or kidney disease.

Before taking tetracycline, tell your doctor if you are taking any of the following drugs:

cholesterol-lowering medications such as cholestyramine (Prevalite, Questran) or colestipol (Colestid);
isotretinoin (Accutane);
tretinoin (Renova, Retin-A, Vesanoid);
an antacid such as Tums, Rolaids, Milk of Magnesia, Maalox, and others;
a product that contains bismuth subsalicylate such as Pepto-Bismol;
minerals such as iron, zinc, calcium, magnesium, and over-the-counter vitamin and mineral supplements;
a blood thinner such as warfarin (Coumadin); or
a penicillin antibiotic such as amoxicillin (Amoxil, Trimox, others), penicillin (BeePen-VK, Pen-Vee K, Veetids, others), dicloxacillin (Dynapen), carbenicillin (Geocillin), oxacillin (Bactocill), and others.

Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat. Stop using tetracycline and call your doctor at once if you have any of these serious side effects:

severe headache, dizziness, blurred vision;
fever, chills, body aches, flu symptoms;
severe blistering, peeling, and red skin rash;
urinating less than usual or not at all;
pale or yellowed skin, dark colored urine, fever, confusion or weakness;
severe pain in your upper stomach spreading to your back, nausea and vomiting, fast heart rate;
loss of appetite, jaundice (yellowing of the skin or eyes); or
easy bruising or bleeding, unusual weakness.

Less serious tetracycline side effects may include:

sores or swelling in your rectal or genital area;
mild nausea, vomiting, diarrhea, or stomach upset;
white patches or sores inside your mouth or on your lips;
swollen tongue, trouble swallowing; or
vaginal itching or discharge.