Azithromycin: what it treats, how to take it, side effects
Last updated September 3, 2026.
Azithromycin is a macrolide antibiotic used to treat infections caused by bacteria. You may know it as a Z-pak or Zithromax. It stops the growth of bacteria, and like all antibiotics it does nothing for colds, the flu, or other viruses.
What does it treat?
Its label covers community-acquired pneumonia, acute bacterial sinusitis, flare-ups of chronic bronchitis (COPD), strep throat in people who cannot take first-line treatment, uncomplicated skin infections, and certain sexually transmitted infections such as chancroid and non-gonococcal urethritis. MedlinePlus adds that azithromycin is used to treat and prevent disseminated MAC infection in people with weakened immune systems, and is sometimes used for travelers' diarrhea, pertussis, and Lyme disease.
How do you take it?
Azithromycin is taken once a day, with or without food, at about the same time each day. The classic 5-day regimen on the label is 500 mg on day 1, then 250 mg once daily on days 2 through 5; for acute bacterial sinusitis the label also allows 500 mg once daily for 3 days. Some infections, like chancroid or non-gonococcal urethritis, are treated with a single 1-gram dose. If you take antacids containing aluminum or magnesium hydroxide, space them apart from your azithromycin dose - ask your pharmacist how many hours to leave between them. If you vomit within an hour of a dose, call your doctor before taking another. Finish the full prescription, and if you miss a dose, take it when you remember unless the next one is close; never double up.
Side effects to know
- Common: nausea, vomiting, diarrhea, stomach pain, and headache.
- Serious: a fast, pounding, or irregular heartbeat; severe skin reactions (rash with fever, blistering, or peeling); liver problems (yellowing of the skin or eyes, dark urine, pain in the upper right stomach, unusual bleeding or bruising); and severe watery or bloody diarrhea, which can appear up to 2 months or more after treatment. Stop taking it and get medical help right away if these occur.
Who should not take it?
If you have ever had jaundice or other liver problems while taking azithromycin, your doctor will probably tell you not to take it again. Before starting, tell your clinician if you or a family member has a prolonged QT interval or any heart rhythm problem, low potassium or magnesium, heart failure, myasthenia gravis, or kidney or liver disease, and if you are pregnant, planning pregnancy, or breastfeeding. Antacids with aluminum or magnesium hydroxide interfere with absorption if taken at the same time.
When is it an emergency?
Call 911 for fainting or a racing, irregular heartbeat, and for signs of anaphylaxis such as trouble breathing or swallowing or swelling of the face, throat, tongue, or lips. Stop the medication and call your doctor immediately for yellowing skin or eyes, dark urine, a blistering rash, or severe or bloody diarrhea. For an overdose, call Poison Control at 1-800-222-1222. Pymander's escalation routing is built and tested specifically for this class of decision; see the safety architecture working paper.
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Common questions
What is a Z-pak?
Z-pak is the brand nickname for a common 5-day azithromycin package (Zithromax). The label regimen is 500 mg on day 1 followed by 250 mg once a day on days 2 through 5, though your prescriber may use a different schedule depending on the infection.
Can I take azithromycin with food?
Yes. Both MedlinePlus and the FDA label say azithromycin tablets can be taken with or without food, whichever your stomach prefers.
Can I take antacids with azithromycin?
Not at the same moment. MedlinePlus advises leaving some time between azithromycin and antacids that contain aluminum hydroxide or magnesium hydroxide, because they can interfere with absorption. Ask your pharmacist exactly how many hours to leave between them.
How fast does azithromycin work?
According to MedlinePlus, you should begin to feel better during the first few days of treatment. If your symptoms are not improving or are getting worse, call your doctor.
Can I drink alcohol while taking azithromycin?
Neither the FDA label nor MedlinePlus lists alcohol as a known interaction with azithromycin. Alcohol can still worsen nausea and slow recovery, so many clinicians suggest avoiding it until you are well - ask your doctor for advice on your situation.
Why does azithromycin keep working after I finish it?
Azithromycin stays in the body far longer than most antibiotics. The FDA label reports a terminal half-life of about 68 hours, which is why a 5-day course keeps acting for several days after the last tablet. This is also why you should still finish the exact course prescribed.