What Happens If I Take Antibiotics When I Do Not Need Them?

Taking antibiotics when you do not need them does not protect you. It actively harms you, and it harms the next person who needs those antibiotics to work. Unnecessary antibiotic use kills off beneficial gut bacteria, triggers side effects ranging from diarrhoea and yeast infections to severe allergic reactions, and — most dangerously — breeds antibiotic-resistant bacteria that can make future infections almost impossible to treat.^[1]

This is not a theoretical concern. The World Health Organization lists antibiotic resistance as one of the greatest threats to global health today.^[2] And the habits driving it — taking antibiotics for colds and flu, keeping leftover courses, stopping treatment early — are happening in every country, every day.

At my counter in Lagos, the most common reason patients take antibiotics they do not need is a belief that stronger medicine works faster. It does not. If your infection is viral, no antibiotic will shorten your illness by a single day. Understanding why starts with understanding what antibiotics are actually designed to do — explained in full in our guide on antibiotics: uses, misuse, and resistance.

What Antibiotics Are — And What They Are Not

Antibiotics are antibacterial agents. They were designed to target bacterial structures — cell walls, protein synthesis machinery, DNA replication enzymes — that exist in bacteria but not in human cells or viruses. That is the whole of it.

A cold? Viral. Flu? Viral. COVID-19? Viral. Most sore throats? Viral.^[3] Giving an antibiotic for any of these is the clinical equivalent of using a fly swatter to fight a fire. And it is worse than simply not working: antibiotics cannot tell the difference between the harmful bacteria you are trying to kill and the hundreds of beneficial bacteria living in your gut and skin. When you take an antibiotic you did not need, you are not doing nothing. You are dismantling a protective ecosystem built up over your entire life.

4 Things That Happen Inside Your Body When You Take Antibiotics You Don't Need

1. Your Gut Microbiome Takes a Hit

Your gut houses roughly 38 trillion bacteria representing hundreds of species.^[4] These bacteria produce vitamins, regulate immune function, protect against pathogens, and maintain the gut lining. Antibiotics — especially broad-spectrum types like ciprofloxacin, amoxicillin-clavulanate, and metronidazole — wipe out large sections of this community indiscriminately.

Research published in Nature found that a single five-day course of ciprofloxacin reduces gut bacterial diversity by up to one third.^[5] Some species may not return to baseline for months. Others never fully recover without probiotic intervention. The gut symptoms — bloating, loose stools, cramping — are the visible sign of this disruption. But the downstream immune consequences are harder to see and longer-lasting.

2. You Are More Likely to Get Diarrhoea

Antibiotic-associated diarrhoea affects between 5% and 35% of people who take antibiotics, depending on the specific drug.^[6] Clindamycin and amoxicillin-clavulanate carry the highest risk. When gut bacteria are wiped out, normal water absorption in the colon is disrupted, and opportunistic organisms — most notably Clostridioides difficile — can proliferate and cause severe, sometimes life-threatening colitis.

For most people, antibiotic-associated diarrhoea resolves when the course ends. But C. diff infection is a different matter — it can persist for weeks, recur multiple times, and in elderly or immunocompromised patients, it can be fatal.^[7] See our full article on how antibiotics cause diarrhoea for more.

3. Yeast Infections Become More Likely

Lactobacillus bacteria colonise the vaginal tract and gut, maintaining the acidic environment that keeps Candida yeast populations in check. When antibiotics clear them out, Candida overgrows.^[8] Vaginal yeast infections affect up to 30% of women after a course of broad-spectrum antibiotics.^[9] Oral thrush is the equivalent in the mouth and throat. Our full explainer on antibiotics and yeast infections covers what to do if this happens.

4. Antibiotic Resistance Develops — In Your Own Body

Every time antibiotics are used, natural selection operates on the bacteria present. The weakest die. The bacteria with any genetic advantage that helps them survive live on, reproduce, and pass that resistance to their offspring.^[1]

And here is the part most people do not hear: resistant bacteria do not stay neatly in one place. They transfer resistance genes horizontally to other species through conjugation — passing resistance like passing a note in a classroom. The resistant E. coli in your gut today can share resistance traits with a Salmonella strain tomorrow. But there is a practical step that helps protect your gut. Read on.

Supporting Your Gut If You Must Take Antibiotics

When antibiotics are genuinely needed, the most evidence-backed strategy for protecting your gut is taking probiotics alongside the course — at least 2 hours apart from each antibiotic dose so the antibiotic does not kill the probiotic bacteria before they reach the gut. Continue for at least 4 weeks after finishing.

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The Broader Problem: What Antibiotic Resistance Actually Means

Antibiotic resistance does not just affect the person who misused the drugs. The resistant bacteria your body generates can spread to family members, to the wider community, through water and food systems. This is a public health emergency, not a personal health matter.

At the current trajectory, drug-resistant infections are projected to cause 10 million deaths annually by 2050 — more than cancer.^[2] We are already losing antibiotics faster than we are developing new ones. And the resistance accumulating in Nigerian hospitals today, in American emergency rooms, in UK GP practices — it was built one unnecessary prescription at a time, in homes, by people who believed they were doing something safe.

For a deeper explanation of why antibiotics cannot touch a virus at all, read our dedicated guide on why antibiotics do not work for viral infections.

Who Is Most at Risk From Unnecessary Antibiotic Use?

Children are particularly vulnerable because their microbiomes are still developing. Early childhood antibiotic overuse has been linked to increased rates of asthma, eczema, obesity, and inflammatory bowel disease in later life — all attributed to microbiome disruption during a critical developmental window.^[11]

Pregnant women face risks both to themselves and to the developing baby. Disruption to the vaginal microbiome during pregnancy increases preterm labour risk, and the altered gut environment can affect the bacterial colonisation the baby receives during birth.^[12]

Elderly patients, immunocompromised individuals, and anyone with a history of C. diff are at significantly elevated risk of severe antibiotic-associated diarrhoea. But no age group is truly safe from the effects of antibiotic misuse.

Myth vs Fact: Common Antibiotic Misconceptions

What Should You Actually Take for a Viral Infection?

What do you take when you feel terrible with a cold or flu and the answer is not an antibiotic? Supportive care — rest, hydration, paracetamol or ibuprofen for fever and pain, saline nasal rinses for congestion, and time. The immune system is built to handle these infections. It needs the right conditions, not a drug that cannot help it.

Zinc lozenges started within 24 hours of symptom onset may modestly reduce cold duration, and vitamin C appears to reduce severity in physically stressed individuals.^[13] Neither replaces rest and hydration. But neither causes harm either.

Seek medical review if any of these appear — because some viral infections do develop bacterial complications:

• Fever above 39°C or lasting beyond 3 days
• Severe facial pain or pressure (possible sinusitis)
• Ear pain or muffled hearing
• Cough producing thick green or brown mucus worsening after day 5
• Feeling significantly worse after initially improving
• Difficulty breathing or swallowing

Frequently Asked Questions

Related Articles

References

1. World Health Organization. (2021). Antibiotic resistance. WHO Fact Sheet. who.int
2. O'Neill J. (2016). Tackling Drug-Resistant Infections Globally. Review on Antimicrobial Resistance. amr-review.org
3. Kenealy T, Arroll B. (2013). Antibiotics for the common cold. Cochrane Database Syst Rev. doi:10.1002/14651858.CD000247.pub3
4. Sender R, Fuchs S, Milo R. (2016). Revised estimates for human and bacteria cells. Cell, 164(3), 337–340. doi:10.1016/j.cell.2016.01.013
5. Dethlefsen L, Relman DA. (2011). Incomplete recovery of the human gut microbiota to repeated antibiotic perturbation. PNAS, 108(S1), 4554–4561. doi:10.1073/pnas.1000087107
6. McFarland LV. (2008). Antibiotic-associated diarrhea: epidemiology, trends and treatment. Future Microbiology, 3(5), 563–578. doi:10.2217/17460913.3.5.563
7. Leffler DA, Lamont JT. (2015). Clostridium difficile infection. NEJM, 372, 1539–1548. doi:10.1056/NEJMra1403772
8. Pirotta MV, Garland SM. (2006). Genital Candida species in women in Melbourne. J Clin Microbiol, 44(9), 3356–3364. doi:10.1128/JCM.00536-06
9. Sobel JD. (2007). Vulvovaginal candidosis. The Lancet, 369(9577), 1961–1971. doi:10.1016/S0140-6736(07)60917-9
10. Laxminarayan R, et al. (2013). Antibiotic resistance — the need for global solutions. The Lancet, 382(9893), 1057–1098. doi:10.1016/S0140-6736(13)62229-6
11. Arrieta MC, et al. (2015). The intestinal microbiome in early life. Front Immunol, 5, 427. doi:10.3389/fimmu.2014.00427
12. Romero R, et al. (2014). Vaginal microbiota of normal pregnant women. Microbiome, 2(1), 4. doi:10.1186/2049-2618-2-4
13. Hemila H, Chalker E. (2013). Vitamin C for preventing and treating the common cold. Cochrane Database Syst Rev. doi:10.1002/14651858.CD000980.pub4

This article is for informational purposes only and does not constitute medical advice. Always consult your pharmacist or doctor before starting any medicine or supplement.