Orlistat side effects: what 25,752 FDA adverse event reports show

Orlistat · 1,022 reaction terms · 61,681 drug–reaction co-reports · data 2026-09-14

Drug class

Intestinal Lipase Inhibitor

FDA label (Established Pharmacologic Class)

Who reports

25,752 reports · 26% serious · 230 with death outcome · 87% female

openFDA FAERS counts, all years, deduplication not applied

Used for

ORLISTAT is indicated for obesity management including weight loss and weight maintenance when used in conjunction with a reduced-calorie diet. ORLISTAT is also indicated to reduce the risk for weight regain after prior weight loss. ORLISTAT is indicat.

FDA label, Indications and Usage

What it is

ORLISTAT is a gastrointestinal lipase inhibitor for obesity management that acts by inhibiting the absorption of dietary fats. Orlistat is (S)-2-formylamino-4-methyl-pentanoic acid (S)-1-[[(2S, 3S)-3-hexyl-4-oxo-2-oxetanyl] methyl]-dodecyl ester.

FDA label, Description section

Boxed warning

None in the current label

How to read this page. FAERS is a spontaneous-reporting system: counts are not incidence rates and a signal is not proof of causation. Each reaction below is run through an automated screen — is the term in the FDA label (known), in the indications (the disease being treated), an administrative/coding term, or none of these (unlabeled)? That screen is mechanical text matching, not a causality assessment. The 30 hand-written Bradford Hill assessments are on the causality assessment page. Not medical advice.

Causality screen of the 40 strongest signals

Labeled adverse reaction 2Labeled (related wording) 3Likely indication confounding 2Reporting / coding artifact 2Lab value / disease marker 2Not in label — unassessed 29

What the badges mean

Labeled adverse reaction The exact term appears in the label's warnings or adverse-reactions sections: a known, expected effect. The FAERS signal confirms the label rather than discovering anything.
Labeled (related wording) The label describes this effect under different wording (e.g. 'neutropenia' for 'neutrophil count decreased'). Treated as known.
Likely indication confounding The term appears in the label's indications: reports probably describe the disease being treated (or its progression), not a drug effect. Classic confounding by indication.
Reporting / coding artifact An administrative, monitoring or exposure term (product issue, off-label use, 'test normal', overdose...). Not a biological reaction; a high PRR here reflects how reports are coded.
Lab value / disease marker A laboratory result, investigation or disease-activity marker (antibody positive, CRP abnormal, swollen joint count) not described in the label. These usually mirror the monitored disease or testing protocol rather than a drug effect; not screened further.
Not in label — unassessed Not found in the label text, not an artifact pattern. This is a genuine candidate for a formal causality assessment (Bradford Hill / WHO-UMC); it has NOT had one here.

Strongest disproportionality signals

Flagged terms (PRR ≥ 2, χ² ≥ 4, n ≥ 10), ranked by PRR; infinite PRRs (no comparator reports) excluded. The EBGM column is a second, shrinkage-based estimate (MGPS) with its 5th percentile EB05 and the BCPNN IC025; a pair flagged by PRR alone is marked PRR-only and should be read as fragile. The strata column recomputes the PRR on serious reports only and flags pairs whose reports are unusually skewed by sex or come mostly from consumers rather than clinicians. 982 further terms are in the interactive explorer. Reaction links open the term's cross-drug page.

Show: hide coding/lab/outcome terms hide indication terms unlabeled only hide PRR-only

Reaction	Reports	PRR 95% CI · ROR · χ²/p	EBGM EB05 · IC025	Label screen	Serious-only & strata	Trial cross-check
Lipiduria	62	4,146.0 2,234.7–7,691.8ROR 4,156.0 · χ² 40,993 / p <1e-300	556.8 EB05 449.9 · IC025 +6.3 3/3 methods agree	Not in label — unassessed	97% consumer	not reported in cached trials
Rectal discharge	2,433	1,588.6 1,484.9–1,699.5ROR 1,754.2 · χ² 1,295,184 / p <1e-300	531.6 EB05 514.1 · IC025 +8.8 3/3 methods agree	Labeled (related wording) related wording	serious n=216 · 99% consumer	not reported in cached trials
Steatorrhoea	1,649	1,332.6 1,232.8–1,440.3ROR 1,423.6 · χ² 824,257 / p <1e-300	498.6 EB05 478.7 · IC025 +8.7 3/3 methods agree	Not in label — unassessed	serious n=158 · 98% consumer	NCT00422058: 5/95 (5.3%) on Orlistat
Change of bowel habit	240	108.1 94.5–123.6ROR 109.1 · χ² 22,346 / p <1e-300	94.7 EB05 85.0 · IC025 +6.1 3/3 methods agree	Not in label — unassessed	serious n=13 · 100% consumer	not reported in cached trials
Hyperoxaluria	17	88.0 53.3–145.2ROR 88.1 · χ² 1,240 / p 5e-272	73.1 EB05 48.4 · IC025 +3.8 3/3 methods agree	Labeled adverse reaction exact term	serious n=16	not reported in cached trials
Anal discomfort	13	74.0 41.9–130.6ROR 74.0 · χ² 791 / p 2e-174	62.0 EB05 38.5 · IC025 +3.3 3/3 methods agree	Not in label — unassessed	serious n=5	not reported in cached trials
Faecal volume decreased	29	51.9 35.7–75.6ROR 52.0 · χ² 1,313 / p 7e-288	47.4 EB05 34.6 · IC025 +4.1 3/3 methods agree	Lab value / disease marker	serious n=4 · 93% consumer	not reported in cached trials
Faecal incontinence	255	44.9 39.6–50.9ROR 45.3 · χ² 10,322 / p <1e-300	42.4 EB05 38.2 · IC025 +5.1 3/3 methods agree	Labeled adverse reaction exact term	serious n=113 · 99% consumer	not reported in cached trials
Salt craving	10	41.2 21.8–77.7ROR 41.2 · χ² 335 / p 3e-75	36.7 EB05 21.3 · IC025 +2.7 3/3 methods agree	Not in label — unassessed	–	not reported in cached trials
Intestinal functional disorder	30	39.9 27.7–57.6ROR 40.0 · χ² 1,048 / p 4e-230	37.3 EB05 27.4 · IC025 +4.0 3/3 methods agree	Not in label — unassessed	100% consumer	not reported in cached trials
Infrequent bowel movements	98	33.3 27.2–40.7ROR 33.4 · χ² 2,913 / p <1e-300	31.8 EB05 26.8 · IC025 +4.5 3/3 methods agree	Not in label — unassessed	serious n=7 · 100% consumer	not reported in cached trials
Faeces pale	84	32.1 25.8–39.9ROR 32.2 · χ² 2,402 / p <1e-300	30.7 EB05 25.6 · IC025 +4.4 3/3 methods agree	Not in label — unassessed	serious n=33 · 85% consumer	not reported in cached trials
Thalamic infarction	22	31.3 20.4–47.9ROR 31.3 · χ² 592 / p 4e-131	29.5 EB05 20.5 · IC025 +3.5 3/3 methods agree	Not in label — unassessed	serious n=22 · 100% clinician	not reported in cached trials
Painful defaecation	24	28.7 19.1–43.1ROR 28.7 · χ² 593 / p 3e-131	27.2 EB05 19.2 · IC025 +3.5 3/3 methods agree	Not in label — unassessed	serious n=13 · 100% consumer	not reported in cached trials
Anal haemorrhage	93	27.9 22.7–34.3ROR 28.0 · χ² 2,308 / p <1e-300	26.9 EB05 22.6 · IC025 +4.2 3/3 methods agree	Not in label — unassessed	serious n=93 · 92% consumer	not reported in cached trials
Food craving	163	27.7 23.7–32.3ROR 27.8 · χ² 4,025 / p <1e-300	26.7 EB05 23.4 · IC025 +4.4 3/3 methods agree	Not in label — unassessed	serious n=26 · 100% consumer	not reported in cached trials
Crystal nephropathy	19	27.2 17.2–43.0ROR 27.2 · χ² 439 / p 8e-98	25.8 EB05 17.4 · IC025 +3.2 3/3 methods agree	Not in label — unassessed	serious n=19	not reported in cached trials
Defaecation urgency	202	24.3 21.1–27.9ROR 24.4 · χ² 4,353 / p <1e-300	23.5 EB05 20.9 · IC025 +4.2 3/3 methods agree	Labeled (related wording) related wording	serious n=58 · 96% consumer	not reported in cached trials
Flatulence (gas)	1,618	23.9 22.8–25.1ROR 25.5 · χ² 34,604 / p <1e-300	23.3 EB05 22.3 · IC025 +4.4 3/3 methods agree	Not in label — unassessed	serious PRR 11.9 · 98% consumer	NCT00422058: 12/95 (12.6%) on Orlistat
Product counterfeit	48	23.9 18.0–31.9ROR 24.0 · χ² 1,002 / p 4e-220	23.1 EB05 18.1 · IC025 +3.8 3/3 methods agree	Reporting / coding artifact	serious n=10 · 91% consumer	not reported in cached trials
Suspected counterfeit product	111	23.6 19.5–28.4ROR 23.7 · χ² 2,308 / p <1e-300	22.8 EB05 19.5 · IC025 +4.1 3/3 methods agree	Labeled (related wording) related wording	98% consumer	not reported in cached trials
Stomach discomfort	147	23.5 19.9–27.7ROR 23.6 · χ² 3,054 / p <1e-300	22.8 EB05 19.9 · IC025 +4.1 3/3 methods agree	Not in label — unassessed	serious n=22 · 97% consumer	not reported in cached trials
Faeces discoloured	603	23.3 21.5–25.2ROR 23.8 · χ² 12,483 / p <1e-300	22.6 EB05 21.2 · IC025 +4.3 3/3 methods agree	Not in label — unassessed	serious PRR 9.0 · 97% consumer	not reported in cached trials
Gastrointestinal disorder	2,186	20.6 19.8–21.5ROR 22.4 · χ² 39,948 / p <1e-300	20.1 EB05 19.4 · IC025 +4.3 3/3 methods agree	Likely indication confounding term in indications; also in warnings	serious PRR 4.4 · 99% consumer	not reported in cached trials
Frequent bowel movements	639	19.8 18.3–21.4ROR 20.3 · χ² 11,120 / p <1e-300	19.3 EB05 18.1 · IC025 +4.1 3/3 methods agree	Not in label — unassessed	serious PRR 12.3 · 98% consumer	not reported in cached trials
Pharmaceutical product complaint	616	19.5 18.0–21.1ROR 19.9 · χ² 10,538 / p <1e-300	19.0 EB05 17.8 · IC025 +4.1 3/3 methods agree	Not in label — unassessed	serious PRR 7.7 · 99% consumer	not reported in cached trials
Abnormal faeces	185	18.8 16.2–21.7ROR 18.9 · χ² 3,026 / p <1e-300	18.3 EB05 16.2 · IC025 +3.9 3/3 methods agree	Not in label — unassessed	serious n=31 · 98% consumer	not reported in cached trials
Nonspecific reaction	107	16.5 13.6–19.9ROR 16.5 · χ² 1,509 / p <1e-300	16.1 EB05 13.7 · IC025 +3.6 3/3 methods agree	Not in label — unassessed	serious n=5 · 100% consumer	not reported in cached trials
Binge eating	21	16.2 10.5–25.0ROR 16.2 · χ² 279 / p 6e-63	15.5 EB05 10.3 · IC025 +2.8 3/3 methods agree	Not in label — unassessed	serious n=5 · 100% consumer	not reported in cached trials
Cerebral venous thrombosis	35	15.9 11.4–22.2ROR 15.9 · χ² 465 / p 2e-103	15.4 EB05 11.4 · IC025 +3.1 3/3 methods agree	Not in label — unassessed	serious n=35 · 100% clinician	not reported in cached trials
Faecal volume increased	10	15.8 8.4–29.5ROR 15.8 · χ² 122 / p 1e-28	13.9 EB05 6.9 · IC025 +2.1 3/3 methods agree	Lab value / disease marker	serious n=6	not reported in cached trials
Hunger	251	15.5 13.7–17.5ROR 15.6 · χ² 3,321 / p <1e-300	15.2 EB05 13.7 · IC025 +3.7 3/3 methods agree	Not in label — unassessed	serious n=17 · 100% consumer	not reported in cached trials
Gastrointestinal sounds abnormal	90	15.2 12.3–18.7ROR 15.2 · χ² 1,155 / p 2e-253	14.8 EB05 12.4 · IC025 +3.4 3/3 methods agree	Not in label — unassessed	serious n=8 · 100% consumer	not reported in cached trials
Menopausal symptoms	39	14.1 10.3–19.4ROR 14.2 · χ² 455 / p 3e-101	13.7 EB05 10.3 · IC025 +3.0 3/3 methods agree	Not in label — unassessed	serious n=34	not reported in cached trials
Weight fluctuation	175	13.9 12.0–16.1ROR 14.0 · χ² 2,047 / p <1e-300	13.6 EB05 12.0 · IC025 +3.5 3/3 methods agree	Likely indication confounding shares a disease stem with the indications wording	serious n=37 · 98% consumer	not reported in cached trials
Gallbladder pain	11	13.6 7.5–24.8ROR 13.6 · χ² 115 / p 5e-27	11.8 EB05 6.1 · IC025 +2.1 3/3 methods agree	Not in label — unassessed	serious n=7	not reported in cached trials
Renal tubular atrophy	13	12.3 7.1–21.2ROR 12.3 · χ² 122 / p 1e-28	10.6 EB05 6.0 · IC025 +2.2 3/3 methods agree	Not in label — unassessed	serious n=13	not reported in cached trials
Frustration	54	12.3 9.4–16.0ROR 12.3 · χ² 540 / p 1e-119	11.8 EB05 9.3 · IC025 +3.0 3/3 methods agree	Not in label — unassessed	serious n=8 · 100% consumer	not reported in cached trials
Treatment noncompliance	805	12.2 11.4–13.1ROR 12.6 · χ² 8,187 / p <1e-300	12.0 EB05 11.4 · IC025 +3.5 3/3 methods agree	Reporting / coding artifact	serious PRR 3.2 · 99% consumer	not reported in cached trials
Premenstrual syndrome	20	12.1 7.8–18.8ROR 12.1 · χ² 190 / p 2e-43	11.1 EB05 7.1 · IC025 +2.5 3/3 methods agree	Not in label — unassessed	serious n=6	not reported in cached trials

Trial evidence (ClinicalTrials.gov)

✓ Trial adverse-event data found on ClinicalTrials.gov

Largest completed trials with posted results that list Orlistat as a study intervention. The right-hand column of the signal table shows whether each FAERS term was also recorded in these trials, with a real denominator (2 of 40 signal terms matched).

NCT00422058 — The Effect of Liraglutide on Body Weight in Obese Subjects Without Diabetes (N=564, PHASE2; 91 AE terms posted; arms: Lira Placebo/Lira 2.4 mg/Lira 3.0 mg; Lira 1.2 mg/Lira 3.0 mg; Lira 1.8 mg/Lira 3.0 mg; Lira 2.4 mg/Lira 3.0 mg)

Caveats: trial populations, doses and follow-up differ from the reporting population; AE terms are sponsor-coded and matched here by wording; absence from a trial list means the term was not reported above the sponsor's frequency threshold, not that it cannot occur.

Most frequently reported reactions

By raw co-report count, regardless of disproportionality. Common terms here are often the illness itself or generic outcomes.

Reaction	Reports	PRR 95% CI · ROR · χ²/p	EBGM EB05 · IC025	Label screen	Serious-only & strata	Trial cross-check
Drug ineffective (drug did not work)	4,543	2.8 2.7–2.9ROR 3.2 · χ² 5,653 / p <1e-300	2.8 EB05 2.7 · IC025 +1.4 3/3 methods agree	Reporting / coding artifact	serious PRR 1.0 · 98% consumer	not reported in cached trials
Rectal discharge	2,433	1,588.6 1,484.9–1,699.5ROR 1,754.2 · χ² 1,295,184 / p <1e-300	531.6 EB05 514.1 · IC025 +8.8 3/3 methods agree	Labeled (related wording) related wording	serious n=216 · 99% consumer	not reported in cached trials
Gastrointestinal disorder	2,186	20.6 19.8–21.5ROR 22.4 · χ² 39,948 / p <1e-300	20.1 EB05 19.4 · IC025 +4.3 3/3 methods agree	Likely indication confounding term in indications; also in warnings	serious PRR 4.4 · 99% consumer	not reported in cached trials
Constipation	1,992	7.6 7.2–7.9ROR 8.1 · χ² 11,335 / p <1e-300	7.5 EB05 7.2 · IC025 +2.8 3/3 methods agree	Not in label — unassessed	serious PRR 3.1 · 97% consumer	NCT00422058: 7/95 (7.4%) on Orlistat; 15/98 (15.3%) control
Diarrhoea (diarrhea)	1,960	2.5 2.4–2.6ROR 2.6 · χ² 1,788 / p <1e-300	2.5 EB05 2.4 · IC025 +1.2 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 2.5 · 92% consumer	NCT00422058: 33/95 (34.7%) on Orlistat; 20/98 (20.4%) control
Weight increased (weight gain)	1,946	7.2 6.9–7.5ROR 7.7 · χ² 10,338 / p <1e-300	7.1 EB05 6.8 · IC025 +2.8 3/3 methods agree	Likely indication confounding term in indications; also in warnings	serious PRR 4.1 · 96% consumer	not reported in cached trials
Steatorrhoea	1,649	1,332.6 1,232.8–1,440.3ROR 1,423.6 · χ² 824,257 / p <1e-300	498.6 EB05 478.7 · IC025 +8.7 3/3 methods agree	Not in label — unassessed	serious n=158 · 98% consumer	NCT00422058: 5/95 (5.3%) on Orlistat
Flatulence (gas)	1,618	23.9 22.8–25.1ROR 25.5 · χ² 34,604 / p <1e-300	23.3 EB05 22.3 · IC025 +4.4 3/3 methods agree	Not in label — unassessed	serious PRR 11.9 · 98% consumer	NCT00422058: 12/95 (12.6%) on Orlistat
Abdominal pain upper	1,374	5.5 5.2–5.8ROR 5.7 · χ² 5,038 / p <1e-300	5.4 EB05 5.2 · IC025 +2.4 3/3 methods agree	Labeled (related wording) related wording	serious PRR 5.7 · 94% consumer	NCT00422058: 1/95 (1.1%) on Orlistat (serious AE)
Headache	1,118	1.5 1.4–1.5ROR 1.5 · χ² 163 / p 1e-37	1.5 EB05 1.4 · IC025 +0.4	Labeled adverse reaction exact term	serious PRR 1.6 · 89% consumer	NCT00422058: 16/95 (16.8%) on Orlistat; 23/98 (23.5%) control
Abdominal distension (bloating)	1,009	8.0 7.5–8.5ROR 8.3 · χ² 6,113 / p <1e-300	7.9 EB05 7.5 · IC025 +2.9 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 4.2 · 96% consumer	NCT00422058: 5/95 (5.3%) on Orlistat; 5/98 (5.1%) control
Nausea	949	1.0 0.9–1.0ROR 1.0 · χ² 0 / p 0.261	1.0 EB05 0.9 · IC025 -0.1 PRR-only: not supported by EBGM or IC	Labeled adverse reaction exact term	serious PRR 1.5 · 84% consumer	NCT00422058: 8/95 (8.4%) on Orlistat; 29/98 (29.6%) control
Treatment noncompliance	805	12.2 11.4–13.1ROR 12.6 · χ² 8,187 / p <1e-300	12.0 EB05 11.4 · IC025 +3.5 3/3 methods agree	Reporting / coding artifact	serious PRR 3.2 · 99% consumer	not reported in cached trials
Malaise (feeling unwell)	782	1.4 1.4–1.6ROR 1.5 · χ² 111 / p 4e-26	1.4 EB05 1.4 · IC025 +0.4	Not in label — unassessed	serious PRR 2.0 · 91% consumer	not reported in cached trials
Abdominal pain	699	2.5 2.3–2.6ROR 2.5 · χ² 605 / p 8e-134	2.4 EB05 2.3 · IC025 +1.2 3/3 methods agree	Labeled adverse reaction exact term	serious PRR 3.6 · 81% consumer	NCT00422058: 1/95 (1.1%) on Orlistat (serious AE)

Unlabeled candidate signals

These flagged terms were not found in the FDA label text and do not match an artifact pattern. They are the pairs that would merit a structured assessment (temporality, dose-response, biological plausibility, consistency across databases, trial or cohort evidence). The screen has not done that; string-matching misses label wording, and a strong PRR can still be stimulated reporting, co-medication, or the disease itself.

Lipiduria — n=62, PRR 4,146.0
Steatorrhoea — n=1,649, PRR 1,332.6 (also seen in trial arm)
Change of bowel habit — n=240, PRR 108.1
Intestinal functional disorder — n=30, PRR 39.9
Infrequent bowel movements — n=98, PRR 33.3
Faeces pale — n=84, PRR 32.1
Thalamic infarction — n=22, PRR 31.3
Painful defaecation — n=24, PRR 28.7
Anal haemorrhage — n=93, PRR 27.9
Food craving — n=163, PRR 27.7

Want to assess one of these properly? The runbook describes the Bradford Hill / trial-evidence workflow used on the assessment page, and handoff_top1000_signals.csv lists the strongest unassessed pairs across all drugs.

Common questions

What are the most reported side effects of Orlistat?

In FDA FAERS, the most frequently co-reported reaction terms for Orlistat are rectal discharge, gastrointestinal disorder, constipation, diarrhoea, weight increased, steatorrhoea. These are report counts, not rates: FAERS has no denominator, reporting is voluntary and uneven, and a term can be reported because of the illness being treated rather than the drug.

Does Orlistat have an FDA boxed warning?

No. The FDA label retrieved for Orlistat has no boxed warning; see the label's Warnings and Precautions for the recognised risks.

Do FAERS signals prove that Orlistat causes these side effects?

No. A disproportionality signal (PRR, ROR) means a reaction is reported more often with this drug than with others in the database. That can reflect a real effect, but also the disease being treated, stimulated reporting after news or litigation, co-medications, or how reports are coded. Causality needs temporality, dose-response, biological plausibility, consistency across data sources and, ideally, trial or cohort evidence. This page screens each term against the FDA label and ClinicalTrials.gov results; it does not establish causation.

Sources & methods

FDA label via openFDA (set ID f81dfaeb-46d5-47ce-9ef6-19259f5ac61c, effective 20260109; matched on openfda.generic_name.exact:"ORLISTAT")
Bayesian shrinkage measures computed offline over all 1,317,300 cached pairs: BCPNN information component (IC, with Norén closed-form IC025) and MGPS empirical-Bayes geometric mean (EBGM, EB05) with a two-component gamma prior fitted by maximum marginal likelihood (α₁=0.57, β₁=0.02, α₂=1.42, β₂=0.70, w=0.17); unstratified
FAERS pair statistics from the OpenPV build of 2026-09-14 (openFDA count= aggregation, field patient.drug.openfda.generic_name.exact, 1,022 reaction terms, min 3 co-reports); PRR/ROR with 95% CI, chi-square with Yates correction
Serious-only and stratified counts (serious:1, patient.patientsex, primarysource.qualification) from openFDA count queries; serious-only PRR uses the drug serious report total and the term global serious total (N_serious=11,882,979); strata shown only when n ≥ 20
Seriousness and sex counts from openFDA count=serious, patient.patientsex, seriousnessdeath
ClinicalTrials.gov API v2 (query ORLISTAT, results-bearing studies sorted by enrollment)

Page generated 2026-10-08. Label and PubChem text are retrieved automatically and may lag the current label; always check the current prescribing information. OpenPV is a beta research tool of the Open Source Medicine Foundation.