Antibiotic Side Effects: What to Expect and How to Handle Them

Starting an antibiotic and worried about side effects? Most people tolerate antibiotics fine, but some experience mild to serious reactions. Knowing what’s common, what’s rare, and what needs immediate care helps you avoid trouble and get the most benefit from treatment.

Common and serious side effects

Common side effects you may see within days include stomach upset, nausea, diarrhea, and mild rashes. Many antibiotics irritate the gut because they change the mix of bacteria there — that can lead to loose stools or yeast infections for some people.

Some antibiotics carry more specific risks. For example, tetracyclines can make you sun-sensitive, so you burn more easily. Fluoroquinolones have been linked to tendon pain or, rarely, tendon rupture — avoid heavy exercise if you get tendon pain. Macrolide antibiotics (like azithromycin) can affect heart rhythm in people with certain conditions or on some heart meds. And a severe allergic reaction — swelling, hives, trouble breathing — is possible with penicillins and other drugs and needs emergency care.

Another risk to watch for is Clostridioides difficile (C. diff) infection: persistent, very watery diarrhea, often with belly pain and fever, that can follow broad-spectrum antibiotics. If diarrhea is severe or bloody, contact your provider right away.

How to reduce risk and when to call the doctor

Simple steps lower your chance of trouble. Take the antibiotic exactly as prescribed. If the label says take with food, do it — food can cut stomach upset. Keep hydrated, avoid tanning beds and long sun exposure with sun-sensitive drugs, and skip strenuous tendon-stressing activities if you’re on a fluoroquinolone and feel any tendon pain.

Probiotics can help reduce the chance of antibiotic-associated diarrhea for some people — Saccharomyces boulardii or Lactobacillus strains are common choices. Start them during or after antibiotics, but ask your provider if you have a weak immune system or serious illness before taking probiotics.

Watch for interactions. Some antibiotics change how other drugs work — for example, antibiotics can increase blood thinning with warfarin, and metronidazole or tinidazole cause a strong reaction with alcohol. Rifampin and a few others can lower hormonal birth control effectiveness, so use extra contraception if you’re told to.

Call your doctor or emergency services if you get trouble breathing, throat or face swelling, a fast-spreading rash, severe diarrhea, high fever, black stools, or sudden sharp tendon pain. For milder side effects, your prescriber may suggest switching drugs, adjusting the dose, or adding an anti-nausea or probiotic to help.

If you have questions about a side effect while taking antibiotics, write down what you notice (symptoms, timing, other meds) before you call. That info makes it easier for your provider to give the right advice. For reliable info on meds and safe use, check trusted sources like your pharmacist or our guides at MyOTCStore.com.