Prebiotic vs probiotic: what is the difference?

The definitions

Both terms have consensus definitions from the International Scientific Association for Probiotics and Prebiotics (ISAPP), an independent scientific group:

Not every fermented food or label that says "live cultures" contains a proven probiotic, and not every fiber is a prebiotic. The benefit has to be shown for that strain or substance. A third term, postbiotic, describes dead or inactivated microbes that still have a documented benefit.

What the evidence shows

Results depend on the exact strain, dose and condition, so a study on one product doesn't carry over to another. The broad picture:

• Diarrhea during antibiotics: the strongest everyday use. Selected probiotics can reduce how often adults get antibiotic-associated diarrhea, and how often and how long children get it. Research suggests certain probiotics may also lower the risk of C. difficile diarrhea, mainly when baseline risk is high, but that evidence is low quality and guideline groups disagree.
• Irritable bowel syndrome: some products may help manage symptoms; results vary by strain.
• "Restoring" gut bacteria after antibiotics: not proven. ISAPP notes a 2023 meta-analysis found probiotics did not preserve gut microbiome diversity during antibiotics.
• Healthy people: there are no formal recommendations for or against probiotics.
• Prebiotics: fibers such as inulin can raise Bifidobacterium, but only if those bacteria are already present. A varied, fiber-rich diet is the best way to support a diverse gut.

Can you take a probiotic with an antibiotic?

Yes, and the studies that showed a benefit started the probiotic early. ISAPP's guidance for clinicians:

1. Start early. Studies typically began the probiotic before or within 1 to 2 days of the first antibiotic dose. Starting later can still help with side effects.
2. Space bacterial probiotics about 2 hours from the antibiotic. Most bacterial probiotics can be killed by antibiotics, so a 2-hour gap may be prudent, as long as the spacing doesn't make you miss doses. No studies have compared timing schedules.
3. Yeast probiotics don't need spacing. Saccharomyces strains are not affected by antibiotics.
4. Keep going afterward. Continuing for 7 to 14 days after the antibiotic ends is a commonly tested approach.
5. Finish the antibiotic as prescribed. There is no evidence that probiotics make antibiotics less effective.

Call a clinician if you have severe or bloody diarrhea, fever or stomach pain during or after antibiotics. These can be signs of C. difficile infection, which needs treatment.

Who should be careful

Probiotics are unlikely to cause harm in healthy people. Gas and bloating can happen in the first few days. Rarely, probiotics have been linked to serious bloodstream infections, mostly in people who were severely ill or immunocompromised.

• People with a weakened immune system, including those taking immunosuppressant drugs
• People who are critically or severely ill
• People with a central IV line (catheter)
• Premature infants

If any of these apply, talk to a clinician before taking probiotics. For people with a chronic disease, Cleveland Clinic suggests asking a doctor or dietitian first.

Choosing between them

Pick the tool for the goal. For antibiotics, a probiotic with a strain studied for that use is the clear choice. For general gut health, start with food: fermented foods plus plenty of fiber. If you try a supplement, choose a product that names its strains and has evidence for the benefit you want; a higher dose isn't necessarily better.

A free Gabriel account pays cost-plus prices on supplements, and Gabriel Core and Plus members get member prices, lower still. Not sure which strain fits? Ask Gabriel free.