To help diagnose giardia infection (giardiasis), your doctor is likely to test a sample of your stool. For accuracy, you may be asked to submit several stool samples collected over a period of days. The samples are then examined in a lab for the presence of parasites. Stool tests may also be used to monitor the effectiveness of any treatment you receive.


Children and adults who have giardia infection without symptoms usually don't need treatment unless they're likely to spread the parasites. Many people who do have problems often get better on their own in a few weeks.

When signs and symptoms are severe or the infection persists, doctors usually treat giardia infection with medications such as:

  • Metronidazole (Flagyl). Metronidazole is the most commonly used antibiotic for giardia infection. Side effects may include nausea and a metallic taste in the mouth. Don't drink alcohol while taking this medication.
  • Tinidazole (Tindamax). Tinidazole works as well as metronidazole and has many of the same side effects, but it can be given in a single dose.
  • Nitazoxanide (Alinia). Because it comes in a liquid form, nitazoxanide may be easier for children to swallow. Side effects may include nausea, gas, yellow eyes and brightly colored yellow urine.

There are no consistently recommended medications for giardia infection in pregnancy because of the potential for harmful drug effects to the fetus. If your symptoms are mild, your doctor may recommend delaying treatment until after the first trimester or longer. If treatment is necessary, discuss the best available treatment option with your doctor.

Preparing for your appointment

While you may initially bring your symptoms to the attention of your family doctor, he or she may refer you to a gastroenterologist — a doctor who specializes in digestive system disorders.

What you can do

Before your appointment, you may want to write a list of answers to the following questions:

  • When did your signs and symptoms begin?
  • Does anything make them better or worse?
  • Do you work or live with small children?
  • What types of medications and dietary supplements do you take?

What to expect from your doctor

During the physical exam, your doctor may ask you to lie down so that he or she can gently press on various parts of your abdomen to check for tender areas. He or she may also check your mouth and skin for signs of dehydration. You also may be given instructions about how to bring in a sample of your stool.

Nov 08, 2022

  1. Leder K, et al. Giardiasis: Epidemiology, clinical manifestations, and diagnosis. https://www.uptodate.com/contents/search. Accessed Nov. 3, 2020.
  2. Parasites — Giardia. Centers for Disease Control and Prevention. https://www.cdc.gov/parasites/giardia/index.html. Accessed Nov. 3, 2020.
  3. Levinson W, et al. Intestinal and urogenital protozoa. In: Review of Medical Microbiology and Immunology. 16th ed. McGraw Hill; 2020. https://accessmedicine.mhmedical.com. Accessed Nov. 3, 2020.
  4. Jameson JL, et al., eds. Protozoal intestinal infections and trichomoniasis. In: Harrison's Principles of Internal Medicine. 20th ed. McGraw Hill; 2018. https://accessmedicine.mhmedical.com. Accessed Nov. 3, 2020.
  5. Bartelt LA. Giardiasis: Treatment and prevention. https://www.uptodate.com/contents/search. Accessed Nov. 3, 2020.


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