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Condition Deep-Dive

Small Intestinal Bacterial Overgrowth (SIBO)

A recognized cause of bloating and IBS-type symptoms, and a contested one. How many people with IBS have it depends almost entirely on the test used: a meta-analysis of 36 studies found 49% positive by lactulose breath test and 19% by glucose1, which is why the headline figures vary so widely.

Gut & Digestive Evidence-Based

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Definition

What Is SIBO?

SIBO occurs when bacteria that normally live in the large intestine migrate and overpopulate the small intestine, where they don't belong.

The small intestine is meant to be relatively sterile, with fewer than 1,000 bacteria per milliliter. In SIBO, counts rise above that level. These bacteria ferment carbohydrates early, producing excessive gas and interfering with nutrient absorption.

There are two established subtypes and a third proposed one, based on the gas produced by the overgrown organisms. Each subtype presents differently and requires a tailored treatment approach (see below).

The stomach and the small intestine coiled inside the large intestine, a close-up circle of too many bacteria in the small intestine, and icons for bloating, diarrhea and abdominal pain

Hydrogen-Dominant SIBO (Hβ‚‚-SIBO)

Generally reported as the most common type, though the split between subtypes varies widely by study and by test method. Caused by gram-negative bacteria such as Escherichia coli, Klebsiella and Proteus species that ferment carbohydrates and release hydrogen gas as a byproduct.

  • β†’Primary symptoms: Loose stools, diarrhea, urgency, explosive gas after meals, watery bloating
  • β†’Timing: Symptoms typically appear 30 to 90 minutes after eating carbohydrates or fiber
  • β†’Breath test: Elevated hydrogen levels (>20 ppm rise) on lactulose or glucose breath test

Methane-Dominant SIBO / IMO

Technically caused by archaea (single-celled organisms), not bacteria, primarily Methanobrevibacter smithii. These organisms consume hydrogen gas and convert it to methane, which slows gut motility.

  • β†’Primary symptoms: Severe constipation, hard pellet-like stools, extreme bloating that doesn't resolve, feeling full for hours after meals
  • β†’Why it's different: Methane gas itself slows the gut. Methane on breath testing is associated with constipation and with measurably slower colonic transit, though whether the amount of methane tracks symptom severity is disputed, and a 2019 study found no correlation with constipation severity2
  • β†’Breath test: Elevated methane (>10 ppm at any point) on breath test
  • β†’Key herbs: Allicin is often used against methane-producing archaea, mainly on laboratory evidence; often combined with berberine and prokinetics

Hydrogen Sulfide SIBO (Hβ‚‚S-SIBO)

A proposed subtype, less established than the other two, produced by sulfur-reducing bacteria such as Desulfovibrio species. Only identifiable with specialized tri-gas breath testing (standard tests miss it). How common it is has not been established.

  • β†’Primary symptoms: "Rotten egg" smelling gas, diarrhea-predominant IBS, sulfur sensitivity, low-flat line on standard breath tests ("flat-line SIBO")
  • β†’Unique feature: Patients often feel worse on high-sulfur foods (eggs, cruciferous vegetables, meat), opposite to Hβ‚‚ SIBO
  • β†’Breath test: Requires tri-gas testing that measures Hβ‚‚S specifically; standard tests appear normal
  • β†’Key approaches: Bismuth, oregano oil, low-sulfur diet; avoid NAC and sulfur-containing supplements initially
By the Numbers

SIBO by the Numbers

19 to 49%
of people with IBS test positive for SIBO: 49% by lactulose and 19% by glucose breath test in a meta-analysis of 36 studies1
~71%
eradication rate with the usual first-line antibiotic across 32 studies and 1,331 patients, on generally poor-quality evidence3
44%
relapsed within 9 months after successful antibiotic treatment4
3
gases a breath test can look for: hydrogen for SIBO, methane for intestinal methanogen overgrowth and hydrogen sulfide, which is not yet widely tested5
Unknown
relapse after herbal treatment has not been measured over a comparable follow-up period6
~34%
of people with digestive complaints who had a breath test were found to have SIBO, in a 2023 review7
Signs & Symptoms

Symptoms of SIBO

Symptoms often worsen 30 to 90 minutes after eating as bacteria ferment food and produce gas. Symptoms outside the gut are often reported alongside it, though how much SIBO explains them is unsettled.

SymptomWhat happens
Digestive Symptoms
Bloating & Visible DistensionThe abdomen visibly swells within minutes to hours of eating, especially after carbohydrates, fiber or other fermentable foods.
Excessive Gas & BelchingFrequent flatulence and belching from bacterial fermentation; the gas may be odorless or foul-smelling.
Altered Bowel HabitsLoose stools with hydrogen-dominant SIBO and constipation with methane, as described under the subtypes above; some people alternate.
Abdominal Pain & CrampingCramping or aching lower abdominal pain, often eased for a while by passing gas or a bowel movement.
Nausea & Loss of AppetiteLow-grade nausea after meals, and feeling full after only a few bites.
Food Intolerances (Multiple)SIBO can reduce brush-border enzymes such as lactase, so lactose and other carbohydrate intolerances may appear alongside it. Links with histamine intolerance and gluten sensitivity are not established.
Systemic & Neurological Symptoms
Brain Fog & Cognitive ImpairmentPoor concentration and mental slowness after meals are commonly described; no explanation for them in ordinary SIBO is established.
Chronic Fatigue & Low EnergyOvergrowth can use up B12 and impair fat absorption, and the resulting deficiencies cause real fatigue that is worth testing for directly. Post-exertional malaise is a different pattern with its own diagnosis and should not be assumed to be SIBO.
Anxiety, Depression & Mood InstabilityAnxiety and low mood are reported alongside SIBO. Gut-made serotonin does not cross into the brain8, and how SIBO might affect mood is not established.
Joint Pain & Body AchesJoint pain and muscle aches are reported alongside SIBO, but a causal link is unproven. Morning stiffness lasting more than an hour is a reason to be assessed for inflammatory arthritis, which is treatable and time-sensitive.
Skin ConditionsRosacea is linked to SIBO: in one study, 46% of 113 people with rosacea had SIBO, against 5% of 60 controls9. No established mechanism links eczema, acne or psoriasis to SIBO.
Nutrient Deficiencies & Weight ChangesSIBO can impair absorption of fat-soluble vitamins, B12 and iron, and prolonged malabsorption can lead to anemia and lower bone density. Unexplained weight loss needs medical assessment.
⚠️ Pattern to watch for: If your symptoms consistently worsen 30 to 90 minutes after eating, especially after carbohydrates, fiber or large meals, SIBO is one possibility, but the same pattern is common in IBS, and no symptom pattern reliably identifies SIBO without testing.
Causes

Causes of SIBO

SIBO develops when the defenses that keep bacteria out of the small intestine fail: the steady movement of its contents, stomach acid, and the valve between the small and large intestine7. Risk also rises with age.

CauseHow It Contributes to SIBOWhat Helps
Slow movement through the small intestineContents that move slowly are not swept clear of bacteria. Causes include nerve damage from diabetes, gastroparesis, systemic sclerosis and chronic intestinal pseudo-obstruction7.Treating the underlying condition, with a prescription prokinetic where needed (conventional care); ginger is used as a prokinetic, though evidence that it prevents relapse is lacking (Supplement Protocol)
Reduced stomach acidStomach acid kills swallowed bacteria. Acid-suppressing medicine raised the odds of SIBO about 1.7-⁠fold across 19 studies10, and stomach surgery weakens the same barrier7.A review with your prescriber of whether acid suppression is still needed (conventional care); do not stop a prescribed medicine on your own
Underactive thyroidThyroid hormones help drive gut movement. In one study, 54% of people with a history of hypothyroidism had SIBO, against 5% of controls11.Diagnosis and treatment of the thyroid condition by your clinician (conventional care)
Surgery that changes the gut's layoutGastric bypass, stomach removal and bowel resections weaken the barriers against overgrowth; one study found SIBO in 43% of people after gastric bypass7.Assessment by the surgical or gastroenterology team, antibiotics, and correction of B12 and other deficiencies (conventional care)
Ileocecal valve problemsWhen the valve between the small and large intestine works poorly or has been removed, colon contents can flow back into the small intestine7.No specific treatment; management follows the general approach, with a low-FODMAP phase to ease symptoms (Nutritional Strategy)
Other gut and liver diseasesSIBO is more common in Crohn's disease, celiac disease, diverticular disease, cirrhosis and pancreatitis7.Treating the underlying disease (conventional care)
Diagnosis

How SIBO Is Diagnosed

Testing is important before committing to an antimicrobial protocol; knowing your subtype guides which herbs are typically chosen.

TestWhat it shows
At-Home Screening Tests
These aren't diagnostic, but strong symptom patterns can guide your next steps before investing in formal testing:
The Carbohydrate ChallengeCompare how you feel 30 to 90 minutes after a high-carbohydrate meal and after a protein-and-fat meal. Symptoms only after carbohydrates point to fermentation, which IBS produces as well as SIBO.
The Overnight Fast TestIf your abdomen is flat in the morning and distended after meals, fermentation of food is a likely contributor, whether from SIBO or IBS.
The SIBO Symptom ChecklistCount the symptoms above that apply, plus unexplained low B12 or iron, or a risk factor listed under Causes. This checklist has not been validated; several points together are a reason to discuss formal testing with a clinician.
Lab & Clinical Tests
Lactulose Breath Test (LBT)You drink a lactulose solution (a non-digestible sugar) after a 24-⁠hour prep diet5. Breath samples are collected every 20 minutes for 2 to 3 hours. Positive: Hβ‚‚ rise >20 ppm or methane >10 ppm. Lactulose is the more sensitive of the two substrates and also the more prone to false positives, which is why a positive result is a reason to investigate further rather than a diagnosis on its own.
Glucose Breath Test (GBT)Similar to LBT but uses glucose, which is absorbed in the upper small intestine. More specific for proximal (upper) SIBO, less sensitive for distal SIBO. A positive glucose test is highly reliable; a negative doesn't rule out SIBO in the lower small intestine.
Tri-Gas Breath Test (Hβ‚‚S included)A breath test that measures all three gases, Hβ‚‚, CHβ‚„ and Hβ‚‚S. Useful if you suspect hydrogen sulfide SIBO (diarrhea-predominant with a flat line on a standard test, sulfur sensitivity).
Comprehensive Stool AnalysisCommercial stool panels cannot detect overgrowth in the small intestine and are not validated for guiding treatment. A standard stool calprotectin test helps rule out inflammatory bowel disease but does not detect SIBO12.
Blood Markers to RequestAsk your doctor about B12, ferritin, albumin and folate, which in SIBO is often high rather than low12, and vitamin D where deficiency is suspected. These indirect markers build the clinical picture alongside breath testing.
Treatment Comparison

Conventional and Holistic Treatment for SIBO

🌿 HOLISTIC
πŸ’Š CONVENTIONAL
🌿

Holistic / Functional Approach

Look for what allowed the overgrowth, support motility and use herbal antimicrobials

Primary Treatment
Herbal antimicrobials (4 to 6 weeks): allicin, berberine, oregano oil or neem
Duration
Usually several months; depends on the cause
Relapse Rate
Not established. No study has followed herbal treatment over a comparable period, so the relapse rate is unknown rather than lower6.
Microbiome Impact
Often described as gentler on commensal bacteria, though this has not been demonstrated. Herbal antimicrobials are not selective.

Full Holistic Approach Includes

  • Herbal antimicrobials: Allicin (450 to 900 mg a day), Berberine (500 mg 2 to 3x/day), Oregano oil. Berberine inhibits CYP3A4 and P-glycoprotein, so it can raise blood levels of many prescription medicines, and it lowers blood sugar on its own. Check with your prescriber before starting it, particularly alongside glucose-lowering medication, an anticoagulant, an immunosuppressant or any drug with a narrow safe range. Not for use in pregnancy or breastfeeding13.
  • Prokinetics: ginger extract or 5-⁠HTP (proposed to stimulate the migrating motor complex, the cleaning wave between meals); do not take 5-⁠HTP with antidepressants, triptans or other serotonin-raising medicines
  • Review of acid-suppressing medicines with the prescriber, since low stomach acid is one recognized SIBO risk factor
  • A low-FODMAP diet during treatment, or an elemental diet (a liquid formula of predigested nutrients) only under medical supervision
  • L-Glutamine + Zinc carnosine, studied for the gut lining (evidence limited)
  • S. boulardii after treatment, studied for microbiome balance
  • Identify and address contributing causes (motility problems, prior antibiotics, diet, stress)
⚠️ Side effects: Stomach upset, nausea and changes in bowel habit are possible. Feeling worse is not a sign it is working; stop and seek advice if symptoms escalate.
Supplement Protocol

Evidence-Based Supplements for SIBO

Evidence for most of these in SIBO is limited; herbal antimicrobials are the best studied, and none of the others has been shown to prevent relapse. Timing matters for each.

Supplement What it is for Typical range Timing Notes & cautions
L-GlutaminePrimary fuel for gut lining cells (enterocytes). Evidence that supplementing it helps SIBO is limited.5 to 10 g/dayFasted, morning or between mealsPowder form best; dissolve in water
NAC (N-Acetyl Cysteine)Breaks down bacterial biofilms in laboratory studies; whether this improves SIBO treatment in people is untested. Also a glutathione precursor.600 to 1,200 mg/day30 to 60 min before antimicrobial doseTake on empty stomach for biofilm action; avoid in Hβ‚‚S SIBO initially
Saccharomyces boulardiiA probiotic yeast. Evidence that it treats SIBO or prevents relapse is limited.250 to 500 mg (about 5 to 10 billion CFU) a dayBetween meals; away from antimicrobials (2+ hrs)Antibiotics do not kill it, as it is a yeast, not bacteria. Use caution with immunosuppression or a central line, as yeast bloodstream infections have been reported; discuss with your team.
Digestive EnzymesSupports complete digestion of food so undigested carbohydrates, proteins and fats don't reach SIBO bacteria for fermentation. Replaces enzymes that SIBO bacteria displace from intestinal brush border cells.1 to 2 capsules per mealAt the start of every mealChoose broad-spectrum: protease, lipase, amylase, lactase, cellulase
Oregano oilContains carvacrol and thymol, potent antimicrobial compounds effective against a wide range of gram-positive and gram-negative bacteria. Commonly used in herbal SIBO protocols, though the evidence base for any individual herb is thin6.100 to 200 mg/day (carvacrol standardized)With meals; enteric-coated preferredEnteric-coated capsules ensure delivery to the small intestine
Allicin (Garlic Extract)The active antimicrobial compound in garlic. Active in laboratory studies against methane-producing archaea (M. smithii). Human evidence is limited. Some studies have looked at it alongside standard antibiotic therapy for methane SIBO, though comparative data is limited.450 to 900 mg/day (allicin-stabilized)With mealsMust be a stabilized allicin extract; ordinary garlic capsules do not provide therapeutic allicin levels
BerberineA plant alkaloid with antimicrobial activity in laboratory studies; evidence in people with SIBO is limited.500 mg 2 to 3x/dayWith mealsSpace doses throughout the day. Berberine inhibits CYP3A4 and P-glycoprotein, so it can raise blood levels of many prescription medicines, and it lowers blood sugar on its own. Check with your prescriber before starting it, particularly alongside glucose-lowering medication, an anticoagulant, an immunosuppressant or any drug with a narrow safe range. Not for use in pregnancy or breastfeeding.
Neem ExtractNeem compounds show antibacterial activity in laboratory studies, and neem has been used traditionally for gut infections; human evidence in SIBO is lacking.300 to 600 mg/dayWith mealsOften combined with berberine and oregano oil. Neem seed oil taken by mouth has caused poisoning with seizures in infants and young children, so keep neem products away from children14. Avoid neem in pregnancy and while trying to conceive: in animal studies, neem extracts acted as a contraceptive and to end pregnancy15.
Peppermint & Lemon OilEnteric-coated peppermint oil is one of the better-evidenced treatments for IBS symptoms, acting as an antispasmodic; it has not been shown to treat SIBO itself. Lemon oil has antimicrobial and anti-inflammatory properties.0.2 mL peppermint oil (enteric-coated) 3x/day30 to 60 min before mealsMust be enteric-coated to reach the small intestine; plain peppermint capsules dissolve in the stomach
Prokinetic, Ginger Root or 5-⁠HTPStimulates the Migrating Motor Complex (MMC), the wave of contractions that sweeps bacteria out of the small intestine between meals. Impaired motility is a recognized SIBO risk factor, but evidence that these supplements prevent relapse is lacking.Ginger: 500 to 1,000 mg; 5-⁠HTP: 50 to 100 mgBefore bed on empty stomachDo not take 5-⁠HTP with antidepressants, migraine triptans or other serotonin-raising medicines, because of the risk of serotonin syndrome.
Curcumin (Turmeric Extract)Anti-inflammatory in laboratory studies, where it downregulates NF-ΞΊB; it has not been shown to treat SIBO.500 to 1,000 mg/dayWith meals containing fatPlain curcumin is poorly absorbed; liver injury has been reported mainly with high-dose, high-absorption formulations such as those with piperine, so stop and seek advice if you notice dark urine or yellowing skin16
Omega-⁠3 Fish OilOmega-⁠3 fats with anti-inflammatory effects; they have not been shown to treat SIBO or its symptoms.2 to 3 g combined EPA+DHA/dayWith mealsUse fish or algal oil at this dose rather than cod liver oil, which also supplies preformed vitamin A, whose adult upper limit is 3,000 mcg a day. Choose a product with independent third-party purity testing17. In heart trials, fish oil supplements raised the risk of atrial fibrillation, an irregular heartbeat, more so above 1 g a day18, so check this dose with your clinician first.
What to Expect

What to Expect Over Time

Treatment clears the overgrowth for many people, but relapse is common, so the timeline runs well past the first course.

Treatment and supportive care, together
First Weeks

A breath test guides treatment. Across 32 studies, an antibiotic course cleared SIBO in about 71%3; herbal protocols run 4 to 6 weeks, with a 46% response in one retrospective study6. A low-FODMAP phase can ease symptoms meanwhile.

Months 1 to 3

Where SIBO was cleared, symptoms improved or resolved in about two-thirds3. Foods are reintroduced one group at a time. In one cohort, 12.6% had relapsed by 3 months4.

Months 3 to 12

Relapse reached 27.5% at 6 months and 43.7% at 9 months, and was linked to older age, previous appendix removal and long-term acid-suppressing medicine4. Correcting the underlying cause and any nutrient deficiency is central12.

Long Term

Where the cause cannot be corrected, repeat treatment may be needed, weighed against the risks of long-term broad-spectrum antibiotics12. B12 and other deficiencies are rechecked.

When to Seek Care

Ask for an urgent appointment for weight loss without explanation, rectal bleeding or bloody diarrhea, a hard lump or swelling in the abdomen, or breathlessness with palpitations and paler skin than usual19.

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Next Steps

Treatment Works, Relapse Is Common

Treatment, chosen after a breath test, clears the overgrowth for many people. A low-FODMAP phase can ease symptoms meanwhile, with foods reintroduced one group at a time. Because relapse is common, correcting the underlying cause and any nutrient deficiency is central.

Explore IBS & IBD β†’ Explore Leaky Gut β†’

References & Evidence Notes

Each numbered entry below is either a source you can follow or a note setting out what the evidence does and does not support. Both are numbered together so the markers in the text line up.

Last reviewed October 20, 2026. Supplement entries are cross-checked against the NIH National Center for Complementary and Integrative Health and the Linus Pauling Institute Micronutrient Information Center.20 This page is nutrition education, not medical advice, and it does not replace your doctor. Two cautions specific to this page. The herbal protocols described here have a much thinner evidence base than the antibiotic treatment they are compared with, and that comparison rests on a single retrospective study whose difference was not statistically significant, see ref. 6. If you take prescription medication, discuss berberine with your prescriber before starting it; it inhibits CYP3A4 and P-glycoprotein and can raise blood levels of many drugs.

  1. The 78% figure often quoted for SIBO in IBS originates in Pimentel M, et al. Am J Gastroenterol. 2000;95(12):3503-⁠3506, which used the lactulose breath test. Later studies report 4 to 78% depending on method. A systematic review and meta-analysis of 36 studies found SIBO prevalence in IBS of 49% (95% CI 40 to 57) with lactulose versus 19% (95% CI 13 to 27) with glucose. PMC10134763. Heterogeneity is largely attributed to the absence of a standardized diagnostic criterion for SIBO. ↩
  2. On methane and motility: Triantafyllou K, Chang C, Pimentel M. Methanogens, methane and gastrointestinal motility. J Neurogastroenterol Motil. 2014;20(1):31-⁠40. jnmjournal.org, and Methane on breath testing is associated with constipation: a systematic review and meta-analysis, PubMed 21286935. The association with constipation and slower transit is reasonably supported; whether the amount of methane tracks symptom severity is not. A later study found breath methane did not correlate with constipation severity or bloating (J Clin Gastroenterol. 2020;54(4):365-⁠369, published online 2019), PubMed 31306344. ↩
  3. On antibiotic treatment: in a meta-analysis of 32 studies with 1,331 adults with SIBO, a poorly absorbed antibiotic cleared the overgrowth in 70.8%, and symptoms improved or resolved in 67.7% of those cleared, though the studies were generally of poor quality, PubMed 28078798. ↩
  4. Lauritano EC, et al. Small intestinal bacterial overgrowth recurrence after antibiotic therapy. Am J Gastroenterol. 2008;103(8):2031-⁠2035. journals.lww.com. In 80 patients treated successfully with standard antibiotic therapy, recurrence was 12.6% at 3 months, 27.5% at 6 months and 43.7% at 9 months. Older age, previous appendectomy and chronic proton-pump-inhibitor use were associated with recurrence. ↩
  5. On breath testing generally, including the limits of lactulose versus glucose substrate and the case for and against the test: Pros and Cons of Breath Testing for Small Intestinal Bacterial Overgrowth and Intestinal Methanogen Overgrowth, Gastroenterol Hepatol. gastroenterologyandhepatology.net. ↩
  6. Chedid V, et al. Glob Adv Health Med. 2014;3(3):16-⁠24, a comparison of herbal therapy against standard antibiotic treatment for small intestinal bacterial overgrowth. PubMed 24891990. Read this one carefully, because the herbal approach on this page rests on it. It was retrospective rather than randomized, and reported a 46% response to herbal therapy against 34% for the antibiotic, a difference that did not reach statistical significance (P = .24). A non-significant difference in a retrospective study is not proof of equivalence, and no randomized trial has confirmed it. The ACG and AGA guidelines build their SIBO recommendations around antibiotics and do not endorse herbal therapy as first-line. The study also reported that 57% of patients who failed antibiotic therapy subsequently responded to the herbal protocol, which is the more useful finding. No study has followed herbal treatment for relapse over the period Lauritano used, so herbal relapse rates are unknown. ↩
  7. On how common SIBO is and what allows it to develop: a 2023 review found SIBO in 33.8% of people with digestive complaints who had a breath test, names slowed movement through the small intestine, reduced stomach acid and backflow through the ileocecal valve as the main causes, found risk rising with age, and reported SIBO in 43% of people after gastric bypass, PubMed 37389240. ↩
  8. The commonly cited figure that roughly 90 to 95% of the body's serotonin is produced in the gut refers to enterochromaffin cells of the GI tract. Gut-derived serotonin does not cross the blood-brain barrier, so the figure describes gut signaling rather than a direct route from gut serotonin to mood. ↩
  9. Parodi A, et al. Small intestinal bacterial overgrowth in rosacea: clinical effectiveness of its eradication. Clin Gastroenterol Hepatol. 2008;6(7):759-⁠764. ScienceDirect. SIBO was present in 52 of 113 rosacea patients (46%) against 3 of 60 controls (5%). One study, one center; treat the tenfold figure as a strong signal rather than a settled number. ↩
  10. On acid-suppressing medicine: a meta-analysis of 19 studies with 7,055 people found proton pump inhibitor use raised the odds of SIBO (odds ratio 1.71), PubMed 28770351. ↩
  11. On thyroid disease: 27 of 50 people (54%) with a history of overt hypothyroidism had SIBO on breath testing, against 2 of 40 controls (5%), PubMed 17698907. ↩
  12. On management: a 2020 gastroenterology expert review advises identifying and correcting underlying causes where possible, correcting nutritional deficiencies and giving antibiotics, while staying mindful of the risks of long-term broad-spectrum antibiotic therapy, PubMed 32679220. ↩
  13. On berberine interactions: it acts on CYP3A4 and P-glycoprotein and can alter plasma levels of co-administered drugs in either direction, PubMed 35048143, and it lowers blood glucose independently. See the NCCIH assessment, ref. 20, and discuss with a prescriber before combining it with prescription medication. ↩
  14. On neem safety: neem seed oil, used as a traditional remedy and sometimes given by mouth to infants, causes toxic encephalopathy with vomiting, drowsiness and recurrent seizures, particularly in infants and young children; deaths and lasting neurological harm have been reported, PubMed 2259944. ↩
  15. On neem and fertility: a 2021 review of 27 studies, almost all in animals, found that neem extracts had antifertility, contraceptive and pregnancy-ending effects, and that clinical studies in people are lacking, PubMed 34092456. ↩
  16. On curcumin and the liver: in a case series and systematic review of acute hepatitis linked to Curcuma longa supplements, every case in the Tuscany series involved high-bioavailability, high-dose formulations, PubMed 32656820. ↩
  17. On cod liver oil and vitamin A: cod liver oil supplements provide vitamin A and vitamin D as well as omega-⁠3s, and the adult upper limit for preformed vitamin A is 3,000 mcg a day, NIH Office of Dietary Supplements. ↩
  18. Gencer B, Djousse L, Al-Ramady OT, Cook NR, Manson JE, Albert CM. Effect of long-term marine omega-⁠3 fatty acids supplementation on the risk of atrial fibrillation in randomized controlled trials of cardiovascular outcomes: a systematic review and meta-analysis. Circulation. 2021;144(25):1981-⁠1990. PubMed 34612056. Seven trials with 81,210 people followed for about 5 years: omega-⁠3 supplements were linked to a higher risk of atrial fibrillation (hazard ratio 1.25), more so in trials of more than 1 g a day (1.49), and the risk rose with each additional gram. ↩
  19. On urgent symptoms: the NHS advises an urgent appointment for unexplained weight loss, bleeding from the bottom or bloody diarrhea, a hard lump or swelling in the abdomen, or shortness of breath with palpitations and paler skin, NHS. ↩
  20. National Center for Complementary and Integrative Health (NIH), nccih.nih.gov, and the Linus Pauling Institute Micronutrient Information Center, lpi.oregonstate.edu/mic. ↩