Antibiotics are among the most important medicines ever developed. They also don’t distinguish between harmful bacteria and the trillions of helpful microbes in your gut.
What happens during a course
Broad-spectrum antibiotics can reduce both the number and diversity of gut bacteria within days. That disruption is why diarrhoea is a common side effect, and why, rarely, harmful bacteria like C. difficile can take hold.
How the gut recovers
In a 2018 study in Nature Microbiology, healthy adults took a four-day course of three antibiotics. Their microbiomes were heavily disrupted at first, then largely recovered within about six weeks. However, some species hadn’t returned even after six months.
Recovery varies with the type of antibiotic, the length of the course, how many courses you’ve had, and your diet.
Supporting recovery
- Eat fiber and varied plant foods, which feed returning bacteria.
- Include fermented foods such as yogurt and kefir.
- Probiotics: certain strains reduce the risk of antibiotic-associated diarrhoea, one of the better-supported uses of probiotics. Ask your pharmacist about timing relative to your doses.
The bigger point
Don’t stop a prescribed course early or avoid antibiotics you need — untreated infections are far more harmful. But it’s reasonable to ask whether an antibiotic is truly necessary: they don’t work on viral infections such as colds and most sore throats, and unnecessary use drives antibiotic resistance.