Immunity · Probiotics

Probiotics for colds: a small, uncertain edge

Much of the immune system lines the gut, so the idea that gut bacteria affect colds is reasonable. The trials point to a modest benefit when probiotics are taken for months, but the certainty is low and the strains vary. Here is what that means in practice.

By Kymata Health Editorial Sources cited inline Prices checked Oct 29, 2026

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Quick answer

The quick answer

Across 23 trials (6,950 people), probiotics may reduce the number of people who get at least one cold (about 24% fewer) and shorten a cold by about a day. Both findings are low certainty.
Probiotics likely reduced antibiotic prescriptions for colds (moderate certainty), which matters because antibiotics do nothing for viral colds.
Most trials used one or two Lactobacillus or Bifidobacterium strains daily for more than three months. A few days of a probiotic when you feel ill is not what was tested.
Benefits are strain-specific and products vary. Choose one that names its strains and states CFU at the end of shelf life.

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Story

Why people try it

Probiotic marketing has moved from "digestion" to "immunity", and many people take one year-round. The question is whether it changes how many colds you get.

The best summary is a 2022 Cochrane review of 23 trials. It found a real-looking signal, but the reviewers rated most of it low certainty, which means the true effect could be quite different.

In depth

What the review found

Low certainty means the reviewers think further research is very likely to change the estimate: trials were small, some had risk of bias, and the strains, doses and populations differed.

At least one cold: risk ratio 0.76 (16 trials, 4,798 people; low certainty).
Three or more colds: risk ratio 0.59 (4 trials; moderate certainty).
Length of a cold: about 1.2 days shorter (6 trials; low certainty).
Antibiotic use for colds: risk ratio 0.58 (6 trials; moderate certainty).
Side effects: no more than placebo (low certainty).

The plan

If you want to try it

Step 1Pick a named-strain product
Look for the strain code (such as L. rhamnosus GG or L. paracasei) and CFU at the end of shelf life.
Step 2Give it the season
Trials ran for three months or more. Start in autumn and judge it in spring.
Step 3Keep the basics
Sleep, vaccines and handwashing still do more. A probiotic is an extra, not a replacement.

The stack

The probiotic option

One optional daily item for the season, with zinc lozenges kept for the first day of a cold. Evidence grade: A strong · B moderate · C limited · D preliminary.

01OptionalPaid links · we earn a commission
Probiotic (named Lactobacillus or Bifidobacterium strains)
Optional. Low-certainty evidence for fewer and slightly shorter colds when taken for months.
What the research shows: Across 23 trials (6,950 people), probiotics may reduce the number of people who had at least one cold (RR 0.76) and shorten an episode by about 1.2 days, both low-certainty evidence. Trials used different strains, so no single product is proven. (PMID 36001877)
- People who are severely immunocompromised, critically ill or have a central line should not take probiotics without their care team.
- Mild gas and bloating in the first week are common.
In the studies
- Most trials in the 2022 Cochrane review used one or two strains at 1 billion to 100 billion CFU a day for more than three months.
A record of what researchers gave, in whom; not a dose for you.
Evidencelimited (Grade C)
Quick pick · Dr. Tobias
Brands that pay us are shown first in this list.
Dr. Tobias Probiotics 30 Billion (30 capsules)
1 capsule: 30 billion CFU including Lactobacillus acidophilus, Bacillus subtilis DE111 and Bacillus coagulans
$26.99price checked Oct 14, 2026 on Dr. Tobias’ site
Shop at Dr. Tobias (paid link, opens in new tab)
We may earn a commission if you buy through these links. That never changes a rank. See how partner links work.
Also from our partners
Only brands that pay us are listed here.
- NOW Foods Probiotic-10, 25 Billion, 30 Veg CapsHerbsPro
  1 veg capsule: 25 billion CFU from a 10-strain probiotic blend (Lactobacillus and Bifidobacterium strains)
  $11.16checked Oct 14, 2026 on HerbsPro’s site
  Shop at HerbsPro (paid link, opens in new tab)
- L. Rhamnosus GGSupersmart
  2 capsules: 10 billion CFU Lactobacillus rhamnosus GG (LifeinU) + 250 mg inulin; 30 servings
  $21checked Oct 11, 2026 on Supersmart’s site
  Shop at Supersmart (paid link, opens in new tab)
- Onnit Total GUT HEALTH (60 capsules)Onnit
  4 capsules: 10 billion CFU probiotic blend (7 strains) and 5 billion CFU Saccharomyces boulardii, with digestive enzymes, betaine HCl and a prebiotic herbal blend; 15 servings
  $23.99checked Oct 20, 2026 on Onnit’s site
  Shop at Onnit (paid link, opens in new tab)
02
Zinc acetate or gluconate lozenges
The one supplement with consistent trial data for a shorter cold, when it is started early. It does little to stop you catching one.
What the research shows: In three pooled zinc acetate lozenge trials (199 adults), colds were about 2.7–2.9 days shorter, against an average cold of 7 days. A 2017 meta-analysis of seven trials (575 people; PMID 28515951) found colds 33% shorter with lozenges giving more than 75 mg a day, with no extra benefit above 100 mg. The 2024 Cochrane review rated the evidence for shorter colds low certainty because trials disagreed, which is why this is a B and not an A. (PMID 27378206, PMID 28515951, PMID 38719213)
- The lozenge trials went above the US upper limit for zinc (40 mg/day from all sources, NIH Office of Dietary Supplements) for a few days only. Weeks of zinc at 50 mg/day or more can lower copper status; do not carry cold-dose zinc into a daily habit.
- Nausea and a bad taste are the common side effects. Zinc nasal sprays and gels have been linked to lasting loss of smell; lozenges dissolve in the mouth and are a different product.
- Separate zinc from quinolone or tetracycline antibiotics (take the antibiotic at least 2 hours before or 4–6 hours after) and from penicillamine.
In the studies
- Trials in the 2017 meta-analysis gave 80–92 mg of elemental zinc a day from lozenges dissolved slowly in the mouth, for up to about a week, in adults with a fresh cold.
A record of what researchers gave, in whom; not a dose for you.
Evidencemoderate (Grade B)
What to look for on the label
Lozenges (not capsules or tablets you swallow) that name zinc acetate or zinc gluconate and the elemental zinc per lozenge, with no citric acid or tartaric acid, which bind zinc in the mouth. Not a nasal spray or gel.
We only name brands we have vetted and work with; a specific pick will appear here once one is approved.

Listed picks above total $26.99 at one-time prices on the brands' own sites; most hold about a month of servings at the label's serving size.

Left out

What we left out, and why

Probiotic shots and drinks with unnamed cultures: Many drinks list "live cultures" without strains or counts. Without a named strain at a studied amount, there is no way to link the product to the trials.

Safety

Safety and interactions

People who are severely immunocompromised, critically ill, recovering from major surgery or who have a central venous line should not take probiotics without their care team; rare bloodstream infections have been reported.
Mild gas or bloating in the first week is common and usually settles.
See a clinician promptly for trouble breathing, chest pain, confusion, a fever lasting more than 4 days, symptoms that improve and then get worse, or symptoms lasting more than 10 days (CDC guidance).
Babies, adults over 65, pregnant women and anyone with asthma, COPD, heart disease, diabetes or a weakened immune system should call early: flu and COVID-19 have prescription options that work best in the first 48 hours.
Not medical advice. Supplements are not evaluated by the FDA to diagnose, treat, cure or prevent any disease.

Questions

Frequently asked questions

Do probiotics help prevent colds?

They may reduce colds modestly. A 2022 Cochrane review of 23 trials found about 24% fewer people had at least one cold with probiotics, but rated the evidence low certainty.

Which probiotic strains were studied for colds?

Mostly Lactobacillus strains (for example L. plantarum HEAL9, L. paracasei) and some Bifidobacterium strains, usually one or two strains at 1 billion to 100 billion CFU a day for more than three months.

Should I take a probiotic when I get a cold?

The trials tested daily probiotics for months before and during the season, not starting one once ill. For a cold that has started, zinc lozenges have better data.

Sources

Studies were checked on PubMed on Oct 31, 2026. Product prices come from each brand's own site, read on Oct 29, 2026; each product shows the date its price was read.

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Probiotics for colds: a small, uncertain edge

Probiotic (named Lactobacillus or Bifidobacterium strains)

Dr. Tobias Probiotics 30 Billion (30 capsules)

Zinc acetate or gluconate lozenges