Anthrax Emergency: How to Take Doxycycline to Prevent Anthrax

Emergency Use Instructions for Recipients

During an anthrax emergency, you will be given a medicine called doxycycline (DOX-i-SYE-kleen) because you may have breathed in anthrax germs. These germs can be deadly. Taking this medicine reduces your chance of getting sick and dying. Until officials know for sure who breathed in the germs, it is important to start taking this medicine as soon as possible after the emergency starts. Public health officials will provide information on who should get the medicine. If you have questions, talk to a doctor or healthcare provider about taking doxycycline.

People who may have breathed in anthrax germs should take the medicine twice a day for 60 days. Most people will be given a 10-day supply to start. Public health officials will tell you whether you need more and how to get it. To reduce your chance of getting sick, take the medicine as long as you are directed and avoid stopping early.

What is anthrax?

Anthrax is a serious disease that can be deadly. You can get sick if you breathe in the anthrax germs. You cannot get anthrax from another person who has anthrax.

  • Early on, you could have any of the following symptoms: fever, chills, tiredness, cough or headache.
  • Later, you could develop shortness of breath, chest discomfort, confusion or nausea. Symptoms usually start within 7 days of breathing in anthrax germs, but can start within 24 hours or take up to 6 to 7 weeks to appear. See a doctor right away if you have symptoms. If you take doxycycline as directed and begin to feel sick anyway or show any of the symptoms mentioned above, get medical care right away.

What is doxycycline?

Doxycycline is a prescription antibiotic approved by the Food and Drug Administration (FDA) to prevent anthrax. FDA is allowing certain uses of doxycycline, including its use without a prescription, during an anthrax emergency. If you were given doxycycline that has an expired date on the container, please note that FDA is allowing the use of certain lots of doxycycline beyond the expiration date on the container based on FDA’s scientific review. For more information, go to the FDA website at www.fda.govexternal icon (search for “doxycycline expiration”).

Who should NOT take doxycycline?

Do not take doxycycline if you have had a severe allergic reaction to doxycycline or similar medicines known as tetracyclines. A severe reaction may include closing of the throat, trouble breathing, or swelling of the lips, tongue or face. Talk to your doctor or public health official about other medicines available to prevent anthrax.

How do I take doxycycline?

For children weighing 76 pounds (35 kg) or more and adults aged 18 years or older:

  • Take 1 pill (100 mg) in the morning with a full glass of water (with or without food or milk) and
  • Take 1 pill (100 mg) in the evening with a full glass of water (with or without food or milk).

The morning and evening doses should be taken 12 hours apart each day for as long as directed.

Doxycycline works just as well whether you take it with or without food or milk.

If you cannot swallow pills, follow the doxycycline tablet crushing and mixing directions which can be also be found by searching “doxycycline crushing instructions” on

For children weighing less than 76 pounds (35 kg), the dose is determined based on weight:

  • Follow instructions provided on the liquid doxycycline label or doxycycline tablet crushing and mixing directions which can also be found by searching “doxycycline crushing instructions” on
  • Take the same amount in the morning and evening (12 hours apart) each day for as long as directed.

Do not skip doses. However, if you miss a dose, do NOT take 2 doses at once. Take the next dose as scheduled.

Keep the pills dry. Store doxycycline pills and liquid at room temperature (between 68–77°F or 20–25°C).

If you get an upset stomach when you take the medicine, take it with food.

Keep doxycycline away from children and pets. Call the poison control center if children or pets ingest the medicine by accident (1-800-222-1222).

What are common side effects of doxycycline?

KEEP taking doxycycline if you have mild nausea, vomiting and/or diarrhea, a mild sunburn or a vaginal yeast infection. If these symptoms become severe, talk to your doctor.

What are possible serious side effects of doxycycline?

Serious side effects from doxycycline are rare. STOP taking doxycycline and get medical care right away (go to the emergency room or call 911) if you have:

  • Closing of the throat or trouble breathing
  • Swelling of the lips, tongue or face
  • Severe itching or rash, especially hives and wheals (red, swollen bumps on the skin)
  • Severe stomach cramps with fever or bloody or watery diarrhea
  • Yellowing of the eyes or skin or dark brown or tea-colored urine
  • Pain when swallowing (esophageal ulcers)
  • Unusual bleeding or bruising
  • Severe headaches, dizziness or double vision

What if I am taking other medicines?

  • Talk to your doctor if you are on a blood thinner like warfarin or seizure medicine like phenytoin. Doxycycline may affect how much of these medicines you need.
  • Doxycycline might not work as well when taken with some medicines. Take doxycycline at least 2 hours before or 2 hours after taking:
    • Multivitamins, supplements or antacids with aluminum, calcium, iron or magnesium
    • Helidac, Kaopectate, Pepto-Bismol or other products with bismuth subsalicylate used for indigestion, nausea or diarrhea

What else do I need to know about doxycycline?

  • It can cause your skin to be more sensitive to the sun. Use sunscreen and cover exposed skin.
  • It can slow bone growth in children.
  • It can make birth control pills less effective. Use a second form of birth control until you finish taking all of your doxycycline.
  • Long-term use can cause discolored teeth or poor tooth enamel in children younger than 8 years and in infants whose mothers took doxycycline during the last half of pregnancy or while nursing.
  • Tell your doctor if you are or become pregnant or are breastfeeding.
  • On rare occasions, doxycycline can cause serious problems. A federal program called the Countermeasures Injury Compensation Program (CICP) may help pay for costs of medical care and other specific expenses of certain people who have been seriously injured by some medicines or vaccines. If you have been injured by doxycycline used to prevent anthrax, you can learn more about this Program by visiting icon or by calling 1-855-266-2427 (toll-free).

What other antibiotics can I take instead of doxycycline?

Public health officials will tell you if other antibiotics (such as ciprofloxacin, levofloxacin or amoxicillin) are available. The risks and benefits of other available antibiotics will be explained in separate instructions.

Risk-Benefit Statement

Although doxycycline has some potential and serious side effects, the expected benefit of doxycycline in helping to prevent disease and death associated with anthrax exposure outweighs these risks.

How do I report side effects or medication errors?

Tell your doctor or healthcare provider right away and report side effects or medication errors to MedWatchexternal icon or 1-800-FDA-1088.

Note: Doxycycline EUI for Recipients (originally issued 03/28/2016; revised 08/18/2017)