Antibiotics are not inherently bad for you, but they do carry real side effects and risks that increase when they’re used unnecessarily or too frequently. Between 5% and 25% of people who take antibiotics develop diarrhea, and repeated courses can disrupt your gut bacteria in ways that take weeks or months to fully recover from. The key distinction is whether the antibiotic is actually needed: when it is, the benefits almost always outweigh the downsides. When it isn’t, you’re absorbing all the risk for zero reward.
Common Side Effects During Treatment
The most frequent complaint during any antibiotic course is digestive trouble. Antibiotics can’t distinguish between the bacteria making you sick and the beneficial bacteria living in your gut, so they damage both. That collateral damage is what causes the nausea, bloating, cramping, and diarrhea that so many people experience. The likelihood varies by drug: broad-spectrum antibiotics, which target a wider range of bacteria, tend to cause more gut disruption than narrow-spectrum ones.
Yeast infections are another common side effect, particularly for women. When antibiotics wipe out bacteria that normally keep yeast populations in check, fungal overgrowth can take hold in the mouth (thrush) or vagina. Skin rashes, sensitivity to sunlight, and general fatigue round out the list of side effects most people encounter. These are typically mild and resolve once the course is finished.
How Antibiotics Affect Your Gut Long-Term
Your intestines house trillions of bacteria that help with digestion, immune function, and even mood regulation. A single course of antibiotics can significantly reduce the diversity of that community. For most people, the gut is resilient enough to bounce back. Research from the University of Alabama at Birmingham suggests the microbiome returns close to its baseline within two to eight weeks after finishing antibiotics, though some subtle shifts can persist longer.
The concern grows with repeated courses. Each round of antibiotics reshuffles the bacterial community, and certain beneficial species may not fully recover. Over time, this can leave gaps that allow problematic organisms to fill in. The most dangerous of these is C. difficile, a bacterium that thrives when normal gut bacteria are depleted. C. difficile releases toxins that damage the lining of the colon, causing severe watery diarrhea that can become life-threatening. Any antibiotic can trigger a C. difficile infection, but certain classes, including fluoroquinolones, clindamycin, cephalosporins, and penicillins, carry a higher risk.
Risks for Children Are Different
The stakes are higher when antibiotics are given early in life. A meta-analysis published in Evolution, Medicine, and Public Health found that antibiotic exposure in the first two years of life significantly increases the risk of developing asthma, eczema, allergies, and childhood obesity. The first six months appear to be the most critical window, which tracks with what scientists know about infant microbiome development: this is the period when the bacterial community is still establishing itself and is most vulnerable to lasting disruption.
The associations were statistically significant across multiple studies, though the effect sizes for obesity were modest. For allergic and atopic conditions like asthma and eczema, the link was stronger. None of this means a child who genuinely needs antibiotics should skip them. It does mean that avoiding unnecessary prescriptions in infancy carries outsized importance compared to later in life.
One Class Carries Uniquely Serious Risks
Fluoroquinolones, a widely prescribed class of antibiotics, carry an FDA boxed warning (the agency’s strongest safety label) for a cluster of disabling and potentially permanent side effects. These include tendon inflammation and rupture, muscle pain and weakness, joint pain and swelling, peripheral nerve damage causing tingling or numbness, and central nervous system effects like confusion or insomnia. These reactions can occur together in the same patient and may not resolve after stopping the medication.
The FDA has emphasized that fluoroquinolones should not be used for uncomplicated infections like sinus infections or urinary tract infections when other options are available. If you’re prescribed one, it’s reasonable to ask whether a different antibiotic would work for your situation.
The Problem With Unnecessary Prescriptions
A major reason antibiotics cause avoidable harm is that they’re frequently prescribed for infections they can’t treat. Antibiotics kill bacteria. They do nothing against viruses, which cause colds, the flu, most sore throats, and most sinus infections. Yet prescribing data from U.S. hospitals shows that roughly 50% of patients admitted with non-COVID viral respiratory infections in 2023 still received antibiotics, and about 35% of COVID-19 patients did as well.
Every unnecessary course exposes you to side effects, disrupts your gut bacteria, and contributes to antibiotic resistance. Resistance happens when bacteria survive exposure to an antibiotic and pass that survival advantage to future generations. Incomplete courses and insufficient doses accelerate this process. The result, over time, is that infections become harder to treat, not just for the broader population but for you personally. The bacteria in your own body can develop resistance, making future infections less responsive to standard treatment.
How to Reduce the Downsides
When you do need antibiotics, there are practical ways to minimize the fallout. Taking a probiotic supplement alongside your antibiotic course can help. A meta-analysis of 15 studies found that probiotics reduced antibiotic-associated diarrhea by about 40%. Multistrain formulas containing three or more bacterial strains were the most effective, roughly twice as protective as single-strain products. Look for supplements containing Lactobacillus, Bifidobacterium, or Saccharomyces strains, and take the probiotic a few hours apart from your antibiotic dose so the antibiotic doesn’t immediately kill the probiotic bacteria.
One important caveat: most probiotic supplements don’t permanently colonize the gut. They pass through, offering benefits only while you’re actively taking them. So continuing the probiotic for a week or two after finishing your antibiotic course is a reasonable strategy.
Beyond probiotics, eating a diverse, fiber-rich diet during and after treatment supports microbiome recovery. Fermented foods like yogurt, kefir, sauerkraut, and kimchi provide live bacterial cultures that can help repopulate your gut. Staying hydrated is straightforward but especially important if you’re experiencing diarrhea.
When the Benefits Clearly Outweigh the Risks
For bacterial infections like strep throat, pneumonia, urinary tract infections, skin infections, and sepsis, antibiotics remain essential and often lifesaving. The risks described above are real but manageable, and they pale in comparison to what happens when a genuine bacterial infection goes untreated. Untreated strep can damage heart valves. Untreated UTIs can spread to the kidneys. Untreated pneumonia can be fatal.
The goal isn’t to fear antibiotics. It’s to use them precisely: take them when they’re genuinely needed, finish the full course as prescribed, skip them when the infection is viral, and support your body’s recovery afterward. That approach gives you the benefits of one of medicine’s most powerful tools while keeping the downsides as small as possible.