Antibiotic Resistance: Why Your Leftover Tablets Are a Bad Idea
Antibiotic resistance is routinely described as a future crisis. It is already a present one, with drug-resistant infections causing a large and rising number of deaths annually, and a substantial share of that is driven by ordinary everyday prescribing and self-medication.
How resistance happens
Bacteria reproduce rapidly and mutate. When antibiotics are used, susceptible bacteria die and resistant ones survive and multiply. That is natural selection operating over hours rather than millennia.
Bacteria also swap resistance genes between species, so resistance acquired by a harmless gut bacterium can transfer to a dangerous one.
Two points follow that are frequently misunderstood:
Your body does not become resistant. The bacteria do. You can acquire resistant bacteria from the environment, from food, or from someone else, having never taken the antibiotic yourself.
Every course of antibiotics contributes, including appropriate ones. The aim is not zero antibiotic use; it is using them only where they help.
What antibiotics do not treat
Antibiotics kill bacteria. They have no effect whatsoever on viruses.
Viral, and therefore not helped by antibiotics:
- The common cold
- Most sore throats
- Most coughs and bronchitis, including when the sputum is green or yellow
- Flu
- Most sinus congestion in the first ten days
- Most cases of gastroenteritis
- COVID-19
The colour of mucus does not indicate bacterial infection. Green or yellow sputum reflects white cells doing their job and occurs in ordinary viral infections. This single belief probably drives more unnecessary prescribing than any other.
When antibiotics are appropriate
- Bacterial pneumonia
- Urinary tract infection with symptoms
- Streptococcal throat infection, confirmed or strongly suspected by clinical scoring
- Bacterial sinusitis, typically symptoms beyond ten days without improvement
- Cellulitis and other skin infections
- Dental abscess with spreading infection
- Sexually transmitted bacterial infections
- Tuberculosis, with specific long combination regimens
- Many surgical prophylaxis situations
The specific habits that drive resistance
Buying antibiotics without a prescription. Widespread in many countries. The person self-selects the drug, usually guesses wrong about whether it is needed, and almost always chooses a dose and duration that are wrong.
Keeping leftovers. If there are leftovers, the course was not completed, which is its own problem. Taking a partial old course for a new illness is close to a worst case: wrong drug, wrong dose, too short, selecting for resistance without clearing anything.
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Sharing antibiotics with family members.
Pressuring doctors for a prescription. Clinicians under time pressure and facing an insistent patient frequently prescribe to end the consultation. Saying “I’d rather avoid antibiotics if they won’t help” changes that dynamic immediately.
Stopping early because you feel better. The modern nuance here is that for some infections shorter courses are now recommended precisely because they reduce resistance. The right answer is to take the course your doctor prescribed, which may be shorter than you expect, and not to extend or shorten it yourself.
Agricultural use of antibiotics for growth promotion in livestock, which is a large contributor and beyond individual control.
What resistance looks like in practice
- Infections that would once have been cured by a cheap oral tablet now requiring intravenous drugs and hospital admission
- Multi-drug resistant tuberculosis, which takes far longer to treat, with more toxic drugs and worse outcomes
- Resistant gonorrhoea
- Carbapenem-resistant organisms in hospitals, where very few options remain
- Routine procedures becoming riskier, because hip replacements, caesarean sections, chemotherapy and transplants all depend on antibiotics working when infection occurs
What you can do
Do not ask for antibiotics for a viral illness. Ask instead what would make the doctor change their mind, and what symptoms should bring you back.
Accept a delayed prescription where offered: a prescription to fill only if things have not improved by a stated point. This reduces antibiotic use substantially without worse outcomes.
Take the course exactly as prescribed, neither extending nor shortening it yourself.
Never use leftover or shared antibiotics. Return unused medicine to a pharmacy.
Get vaccinated. Influenza, pneumococcal, COVID-19 and routine childhood vaccines prevent infections that would otherwise be treated with antibiotics. Vaccination is one of the most effective anti-resistance measures available.
Hand hygiene, which prevents infection transmission directly.
Food safety: cook meat thoroughly, separate raw and cooked, wash produce.
Ask about the duration. Many conditions are now treated with shorter courses than they were a decade ago.
Probiotics and the gut after antibiotics
Antibiotics disrupt the gut microbiome, sometimes for months. Diarrhoea is common, and in some cases Clostridioides difficile infection follows, which can be severe.
Evidence for probiotics preventing antibiotic-associated diarrhoea is reasonable for certain strains, though not uniform. Eating a varied high-fibre diet with fermented foods during and after a course is sensible regardless.
Report severe, watery or bloody diarrhoea during or after antibiotics rather than treating it as expected.
The short version
Antibiotics do nothing for colds, most coughs and most sore throats, and green mucus is not evidence of bacterial infection. The habits that matter most are not buying them over the counter, not keeping or sharing leftovers, not pressing a doctor for them, and taking exactly the course prescribed.