Azithromycin (Z-Pak): uses, the 5-day course and side effects

By the Medsmingle Team · Updated 13 November 2026

This is a prescription medicine. Only take it if it has been prescribed for you after a medical assessment, and follow your doctor’s and pharmacist’s instructions.

Azithromycin (Zithromax) is a macrolide antibiotic used for some chest, sinus, ear, throat and skin infections, and certain sexually transmitted infections. The familiar “Z-Pak” is a 5-day course.

How the course works

One regimen used for certain adult infections is 500 mg on day 1, then 250 mg on days 2 to 5; this is not suitable for every infection or person. Follow your own prescription. Azithromycin stays in the tissues, so it keeps working for several days after the last pill.

Side effects

• Diarrhea, nausea, stomach cramps
• Headache
• Changes in taste

Serious warnings

• Heart rhythm: can prolong the QT interval. Tell your doctor if you have heart rhythm problems, low potassium or magnesium, or take medicines that affect heart rhythm. Get urgent help for fainting or a racing, irregular heartbeat
• Severe watery or bloody diarrhea, during or after the course (C. diff)
• Yellow skin or eyes
• Serious rash or swelling

When it’s not the right choice

Antibiotics don’t help colds, flu or most sore throats and coughs. Overuse of azithromycin has increased resistance, so doctors reserve it for infections where it works.

Interactions

• Antacids with aluminum or magnesium: ask your pharmacist about timing for your specific formulation
• Warfarin: may need closer monitoring

Frequently asked questions

Can I drink alcohol on azithromycin?

Moderate alcohol doesn’t interact directly but may worsen stomach upset.

For questions about a prescription or symptoms, speak with your own doctor or pharmacist. For website enquiries, contact our team.

General information only. It isn’t a substitute for advice from your doctor or pharmacist.

Source

MedlinePlus patient medicine information. This overview does not list every warning or interaction.