What Really Happens to Your Body When You Take a Z-Pak

If you've ever had a bacterial infection, there's a pretty good chance you've been prescribed a Z-pak.

Short for Zithromax or Zmax — brand names for the antibiotic generically known as azithromycin — the term "Z-pak" simply refers to a specific packaging and dosage of this commonly used antibiotic, says Ilana Richman, MD, a Yale Medicine internist and assistant professor of medicine at Yale School of Medicine.

Azithromycin can be used to treat a variety of bacterial infections, per the Mayo Clinic. It's a versatile drug that can be prescribed for respiratory, skin, dental and sexually transmitted infections, among others.

But for a number of reasons, Z-paks (and azithromycin more generally) tend not to be prescribed as often as they used to.

Below, what to know about this medication, including side effects to look out for if your doctor does suggest you take it.

As a pre-packaged dose pack of azithromycin, Z-paks are part of the macrolides antibiotic family, according to the National Library of Medicine.

"They work by stopping bacteria from being able to grow," explains Sarah C. Nosal, MD, FAAFP, a family physician in New York and member of the board of directors of the American Academy of Family Physicians.

Unlike many antibiotics, which typically have a seven-day or longer course, Z-paks deliver a shorter and more efficient five-day treatment: You take two pills on the first day, then one pill each day for the next four days, per the FDA.

As with all antibiotics, azithromycin is appropriate to take only if you have a true bacterial infection. "Azithromycin has no effect on viruses like those that cause the flu, COVID or the common cold," Dr. Richman says.

But perhaps due to their ease of use, the quick fix they seem to offer or their memorable name, there's a lot of confusion about what Z-paks actually should be used for (again, they can't help cold symptoms), and many people ask for this drug in situations where it isn't needed, Dr. Nosal notes.

In other words, it's more common for someone to ‌think‌ a Z-pak will help them feel better than it is to actually need one.

"Azithromycin is a really important tool for treating certain types of infections," Dr. Nosal says. "But most of the time, a Z-pak is not the first line [treatment] for any of the things we tend to associate it with in our head."

That includes conditions such as bronchitis and sinusitis, which Dr. Nosal points out can be viral rather than bacterial more often than not.

A big reason why providers may not prescribe Z-paks as often as they used to is the fact that some studies, including a large May 2012 study in ‌The New England Journal of Medicine‌, have shown a link between azithromycin and serious cardiac events such as abnormal heart rhythms or heart attack.

As a result, in 2013 the Food and Drug Administration (FDA) issued a warning about azithromycin and these possible side effects. People with existing QT interval prolongation, low blood levels of potassium or magnesium, a slower-than-normal heart rate or who are taking certain drugs to treat abnormal heart rhythms may be more at risk, the FDA said.

Since then, penicillin and cephalosporin antibiotics have tended to be the first-line treatments for someone who needs antibiotics for a true bacterial infection rather than azithromycin, says Dr. Nosal.

Antibiotic resistance, which the Centers for Disease Control and Prevention (CDC) calls "an urgent global public threat," may also be contributing to a decline in Z-pak prescriptions.

"In recent years, there has been rising antibiotic resistance to azithromycin, which means that azithromycin doesn't work well to treat some bacterial infections," says Dr. Richman.

All this is to say that your chances of being prescribed a Z-pak are likely lower than they were a decade-plus ago ("I haven't personally prescribed a Z-pak in more than two years," Dr. Nosal estimates).

But there are still situations in which your provider may determine you need azithromycin and specifically a Z-pak, particularly if you're allergic to other antibiotics like penicillin. If that happens, there are some side effects to look out for once you start taking the medication:

Nausea, vomiting and general stomach discomfort are some of the most common side effects you could experience on a Z-pak or any other azithromycin medication.

"The azithromycin family do cause a lot of GI upset," says Dr. Nosal. "They're really good at penetrating tissue, which is part of why they work, but it's common that you're going to get some nausea."

To help make the medication easier to tolerate, Dr. Nosal recommends staying hydrated, having some food in your stomach before each dose (Dr. Richman suggests something bland like crackers) and avoiding anything that could irritate your stomach further, especially alcohol.

You can also work with your doctor to find the best time of day to take your medication: "This is really patient-specific," Dr. Nosal says. "Some people do better taking a Z-pak with a little food in the morning, and some people do better taking it at night and then going to sleep and experiencing less of the GI upset symptoms."

According to the Cleveland Clinic, GI side effects are usually mild enough not to require medical attention. But if they're bothersome, let your provider know, especially if they don't improve or get worse.

You should also let your doctor know if you vomit within one hour of taking your first dose, the National Library of Medicine (NIH) says. The concern here is that you may not have absorbed enough of the medication, Dr. Nosal explains, so check in to see if you might need an additional dose.

As with GI upset, diarrhea is usually mild and short-lived as your body adjusts to the Z-pak medication, but reach out to your provider if it's prolonged or severe, or if you're experiencing fever or stomach cramps.

Your best bet is to avoid diarrhea medications while taking a Z-pak unless your provider specifically recommends them, according to the Mayo Clinic.

Also important: Side effects like diarrhea and nausea are common reasons why people stop taking antibiotics mid-course, Dr. Nosal says. But if they're causing you to consider skipping the rest of your Z-pak doses, it's critical you reach out to your provider, who can work with you to find a way to finish your prescription.

"It's important to complete your Z-pak so you're able to defeat the bacteria and don't end up with resistance," Dr. Nosal says.

A lot of antibiotics can cause sun sensitivity, says Dr. Nosal, and that includes azithromycin.

Luckily, the short course of a Z-pak means your risk is less than that of someone who is taking antibiotics for a prolonged period of time, but you could still get burned more easily while taking it.

"I would not start a Z-pak then go to the beach for the next five days," says Dr. Nosal. "You would be at much greater risk of sunburn than usual."

A headache is one of those side effects that tends to be a possibility for most medications, says Dr. Nosal. Staying hydrated can help, and if you're uncomfortable you can take an over-the-counter pain reliever like Tylenol or ibuprofen (just check with your provider to make sure you don't have any contraindications with another medication you're taking).

Luckily, "I haven't had anyone ever had such a severe headache [from a Z-pak] that they couldn't take it," says Dr. Nosal.

Still, as with any side effect, let your provider know if your pain is severe.

The most common Z-pak side effects — such as nausea, vomiting, diarrhea and headache — should only last as long as you're taking the medication, Dr. Richman says. So if you're dealing with some GI discomfort, for example, you should be feeling better within a few days.

If your side effects linger after you've completed your Z-pak or are severe, though, you should let your doctor know.

Happily, the most common Z-pak side effects, such as nausea, diarrhea and headache, can be managed at home. Dr. Nosal suggests doing the following:

• Drink plenty of water to stay hydrated
• Eat something before taking your medication
• Reach for over-the-counter pain relievers if you need them

While most azithromycin side effects don't require medical treatment, you should reach out to your doctor right away if you have any of the following symptoms, which could be a sign of something more serious, according to the National Library of Medicine:

• Dizziness
• Fast, irregular heartbeat
• Rash, hives, blisters or peeling skin
• Itching skin
• Yellowing skin or eyes
• Wheezing or difficulty breathing
• Swelling
• A hoarse voice
• Extreme tiredness
• Flu symptoms
• Unusual bleeding or bruising
• Dark urine
• Loss of energy or appetite
• Pain in your upper stomach

Because of the rare but significant risks of fatal heart rhythms while taking azithromycin, it's particularly important to be aware of the possible signs of an arrhythmia.

"If you start to feel palpitations, your heart is racing, you are lightheaded or have chest pain, stop the antibiotic and see your doctor," says Dr. Nosal. "Don't hesitate: Those are really critical reasons to be evaluated right away."