When Should You Not Take a Probiotic? Who Should Take Care and Why

Do not start a live-culture product without asking your clinical team if you have a weakened immune system, are seriously ill or in hospital with a central line, are caring for a premature baby, or have been told by your doctor not to; speak to a midwife or GP first if you are pregnant or breastfeeding.^{1, 2, 3} For everyone else the pooled trials found side effects no more common than on placebo (relative risk 1.00 across 36 antibiotic trials in 9,312 adults), and the NHS page says that for most people "probiotics appear to be safe".^{4, 5} One spoke of the Wellgard probiotics guide: the safety canonical.

Evidence at a glance

• Trials: 3 pooled analyses of adverse events (the largest 37 trials, 11,911 people) and 4 case series (89, over 200, 10 and 7 patients).^{6, 7, 8, 9, 2}
• Largest single trial: 2,981 UK inpatients aged 65 and over, 21 days, no serious adverse event attributed to it.¹⁰
• Strongest measured outcome: adverse events in 10.9% on live cultures against 12.2% on placebo across 37 trials (RR 0.86, moderate certainty).⁶
• Not tested: the four groups themselves; the trials behind the safety record excluded them.

Sources checked on 16 October 2026.

When should you not take a probiotic?

When you are in one of four groups, and the reason is case series rather than trials. People with a weakened immune system: a 2014 review of 17 studies in 1,530 people with cancer found five case reports of bloodstream infection linked to live-culture products and concluded they "may be a rare cause of sepsis".¹ People who are seriously ill or in hospital with a central line: in a Belgian series of ten Saccharomyces cerevisiae bloodstream infections, 80% of patients were on tube or drip feeding, 70% had a central line, six had been prescribed an S. boulardii product, and half died.⁹ Premature babies: in a series of seven yeast bloodstream infections in two intensive care units, two patients were premature newborns, and the blood isolates were 96.4 to 99.7% identical to the S. boulardii products the patients were taking.² And anyone whose doctor has said so. The Lactobacillus record is the same shape: in a Finnish series of 89 bloodstream infections, 82% of patients had severe or fatal underlying disease, the predisposing factors were immunosuppression, long hospital stays and surgery, and in 11 cases the strain matched a widely used commercial strain.⁷ In a healthy person this is not a documented risk; the NHS says that with "a weakened immune system, you should talk to a doctor".⁵

Who are the three people who should not take probiotics?

People whose immune system is suppressed, people who are critically ill or have a central venous line, and premature infants; the fourth is anyone whose doctor has said so. A 2015 review puts the general position plainly: "probiotics have been used safely for years", safety outcomes are "inconsistently reported" in trials, and the theoretical risks in case reports include systemic infection in susceptible people.³ Age alone is not on the list, but the Belgian authors suggested older age as a contraindication for yeast-based products after three of their ten cases were aged 80 or over with no other risk factor.⁹

Who should not take acidophilus?

The same four groups; Lactobacillus acidophilus is not a special case. In a review of over 200 reported Lactobacillus infections, the species most often involved were L. casei and L. rhamnosus, the infections were mostly endocarditis and bacteraemia, and overall mortality was nearly 30%, concentrated in people with other infections at the same time.⁸ What acidophilus is good for has its trials; the first-days wind and looser stools are the same for any species (side effects of too much probiotics).

Can you take probiotics with antibiotics or antifungals?

With antibiotics, yes: the trials that counted fewer cases of diarrhoea started the culture within the first two days of the course. Many antibiotics kill bacterial cultures, which is why packs suggest a gap of a few hours; no trial has tested that gap, and in the 36 adult trials the lower diarrhoea rate held whatever the interval.⁴ Saccharomyces boulardii is a yeast, so an antifungal medicine (clotrimazole, fluconazole or nystatin, for example) acts on it: in the seven-case series the isolates were "susceptible to all antifungal agents tested".² A pharmacist sets any spacing; no prescribed medicine is moved or stopped for a supplement. In full: live cultures with antibiotics.

Can I take probiotics while on infliximab or other immune-suppressing medicines?

Ask the prescribing team first, because this is the group the case series describe. Infliximab, adalimumab, methotrexate, azathioprine, ciclosporin, tacrolimus, high-dose steroids and chemotherapy all lower the body's defence against the organisms in a capsule; the culture is the question, not an interaction. We found no randomised trial of a live-culture product in people taking infliximab; the record is the immunocompromised case reports above.^{1, 7} The prescribing team knows the condition the medicine is for, which matters as much as the medicine.

Why do cardiologists warn against probiotics?

Because of case reports of heart-valve infection, not any trial. In the review of over 200 Lactobacillus infections, endocarditis was one of the two commonest presentations, in people with existing valve disease or other serious illness.⁸ The large trials in healthy adults show no such signal: adverse events matched placebo across 36 antibiotic trials and 23 respiratory trials.^{4, 11} "Cardiologists" is the question's word, not a finding; anyone with a heart-valve condition, a replacement valve or a history of endocarditis asks their cardiologist first. Blood pressure is in the FAQ below.

Should you take probiotics if you have gastroparesis?

Ask your GP or gastroenterology team; the record is one small study. In a manufacturer-funded Japanese trial, 28 adults with mild to moderate delayed gastric emptying ate a yoghurt with one L. gasseri strain or a strain-free yoghurt for 12 weeks; the odds of improved emptying were 4.1 times placebo, with a confidence interval from 0.8 to 20.2 that includes no effect, and the authors said the data "were not enough" to support a benefit.¹² Gastroparesis as diagnosed has no trial of live cultures that we found, so the team managing it decides.

Can I take probiotics without asking a doctor?

A healthy adult can, within the pack's instructions; the four groups, anyone pregnant or breastfeeding and anyone on medication ask first. The NHS page, last reviewed 24 November 2022 and past its review date, says that someone with "an existing health condition or a weakened immune system" should talk to a doctor first.⁵ Can I take probiotics without asking a doctor takes the question further.

Pregnancy and breastfeeding

Speak to a midwife or GP before starting. Live cultures were well tolerated in pregnancy trials: a 2021 review of 100 eligible studies found no serious adverse effect to mother or infant among the 11 that reported adverse effects, with one trial recording more vaginal discharge and stool changes (RR 3.67).¹³ But a 2021 Cochrane review of seven trials in 1,647 women given live cultures to lower the chance of gestational diabetes found pre-eclampsia more common among the women who took them (RR 1.85, 1.04 to 3.29; four trials, 955 women; high-certainty evidence), and its authors "urge caution".¹⁴ Nothing here recommends a live culture in pregnancy; the intimate-health questions are on BV, thrush and UTIs in pregnancy.

Children

A GP or health visitor first. In 33 trials in 6,352 children on antibiotics, live cultures cut diarrhoea from 19% to 8% with adverse events low and none serious; the same review notes serious events reported outside trials in severely debilitated or immunocompromised children with central lines.¹⁵ Premature and very unwell babies are the group above.

What we don't know

• No study gives a rate of serious infection in supplement users within the four groups; case series have no denominator.
• No pharmacokinetic study pairs any live culture with any medicine; "no recorded interaction" means unstudied.
• No trial has tested live cultures in diagnosed gastroparesis.¹²
• No trial in people with heart-valve disease exists in either direction.

Frequently asked questions

Do probiotics raise blood pressure?

No record says so. A 2014 pooled analysis of nine randomised trials found systolic blood pressure 3.56 mmHg lower on live cultures than on control, a modest change seen only in trials of eight weeks or more; the pooled adverse-event data report no rise.^{16, 4}

Can you take probiotics with blood pressure medication?

No interaction study exists for any live culture with any blood-pressure medicine, and none is reported in the pooled trials; ask the pharmacist, and never change the medicine for a supplement.⁴

Can you be allergic to probiotics?

To the culture itself, rarely; to what sits beside it, more plausibly: some products carry milk, soya or wheat traces from the growth medium or filler, and the label's allergen line is the check. Swelling of the face or mouth or difficulty breathing is a 999 call. In the children's trials, adverse events, rash among them, ran at 4% on live cultures against 6% on placebo.¹⁵

What are the side effects of taking acidophilus?

The same early wind, bloating and looser stools as any live culture, no more common than placebo in the pooled trials; worse before better has the detail.⁴

Sources

1. Redman MG, et al. Systematic review, 17 studies, 1,530 people with cancer in the safety analysis. 2014. PubMed 24618152.
2. Roy U, et al. Case series, 7 intensive-care patients with yeast bloodstream infection, two hospitals. 2017. PubMed 28133894.
3. Doron S, et al. Narrative review of the risk and safety of live cultures. 2015. PubMed 25922398.
4. Liao W, et al. Pooled analysis, 36 randomised trials, 9,312 adults. 2021. PubMed 33234881.
5. NHS. Probiotics. nhs.uk/tests-and-treatments/probiotics. Page last reviewed 24 November 2022 (review overdue).
6. Esmaeilinezhad Z, et al. Cochrane review; adverse events in 37 randomised trials, 11,911 people. 2025. PubMed 40931979.
7. Salminen MK, et al. Case series, 89 Lactobacillus bloodstream infections, Finland. 2004. PubMed 14679449.
8. Cannon JP, et al. Literature review, over 200 reported Lactobacillus infections. 2005. PubMed 15599646.
9. Poncelet A, et al. Case series, 10 patients with Saccharomyces bloodstream infection, one Belgian hospital, 2005 to 2017. 2021. PubMed 33934809.
10. Allen SJ, et al. PLACIDE. Randomised trial, 2,981 UK inpatients aged 65 and over, 21 days; NIHR funded. 2013. PubMed 23932219.
11. Zhao Y, et al. Cochrane review, 23 randomised trials, 6,950 people. 2022. PubMed 36001877.
12. Ohtsu T, et al. Randomised double-blind trial, 28 adults with delayed gastric emptying, 12 weeks; manufacturer-funded, one author employed by the maker. 2021. PubMed 34071718.
13. Sheyholislami H, Connor KL. Systematic review, 100 eligible pregnancy and lactation studies, 11 reporting adverse effects. 2021. PubMed 34371892.
14. Davidson SJ, et al. Cochrane review, 7 randomised trials, 1,647 pregnant women. 2021. PubMed 33870484.
15. Guo Q, et al. Cochrane review, 33 randomised trials, 6,352 children. 2019. PubMed 31039287.
16. Khalesi S, et al. Pooled analysis of blood pressure, 9 randomised trials. 2014. PubMed 25047574.

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