L-Lysine side effects: what 731 FDA adverse event reports show

L-Lysine · L-Lysine 7415 · 18 reaction terms · 104 drug–reaction co-reports · data 2026-09-14

Drug class

Not stated in label

Brand names

L-Lysine 7415

openFDA label

Who reports

731 reports · 53% serious · 15 with death outcome · 78% female

openFDA FAERS counts, all years, deduplication not applied

Used for

For the temporary relief of itchy, painful, red, or irritated skin, anxiousness, diarrhea, or indigestion.

FDA label, Indications and Usage

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 9 strongest signals

Reporting / coding artifact 1No label text to screen 8

What the badges mean

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.
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.
No label text to screen No validated FDA label was retrievable for this product, so the screen could not run. Disproportionality only.

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. 9 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
Mouth ulceration	12	16.4 9.4–28.7ROR 16.7 · χ² 158 / p 1e-36	15.3 EB05 8.4 · IC025 +2.4 3/3 methods agree	No label text to screen label has no adverse-reaction text	serious PRR 11.9	no trial data cached
Oral herpes	11	16.3 9.0–29.2ROR 16.5 · χ² 143 / p 3e-33	15.0 EB05 7.9 · IC025 +2.3 3/3 methods agree	No label text to screen label has no adverse-reaction text	serious PRR 7.6	no trial data cached
Hair texture abnormal	7	14.9 7.1–31.2ROR 15.0 · χ² 77 / p 7e-19	12.0 EB05 5.0 · IC025 +1.6 3/3 methods agree	No label text to screen label has no adverse-reaction text	serious n=2	no trial data cached
Gastrointestinal pain	5	13.1 5.5–31.4ROR 13.2 · χ² 45 / p 1e-11	8.8 EB05 3.3 · IC025 +1.1 3/3 methods agree	No label text to screen label has no adverse-reaction text	serious PRR 21.8	no trial data cached
Tendonitis	7	12.9 6.2–27.0ROR 13.0 · χ² 66 / p 3e-16	9.9 EB05 4.3 · IC025 +1.5 3/3 methods agree	No label text to screen label has no adverse-reaction text	serious PRR 18.0	no trial data cached
Oral pain	10	12.8 6.9–23.7ROR 13.0 · χ² 97 / p 3e-23	10.8 EB05 5.4 · IC025 +2.0 3/3 methods agree	No label text to screen label has no adverse-reaction text	serious PRR 12.8	no trial data cached
Impaired driving ability	5	12.6 5.3–30.2ROR 12.7 · χ² 43 / p 3e-11	8.3 EB05 3.2 · IC025 +1.1 3/3 methods agree	No label text to screen label has no adverse-reaction text	serious PRR 18.4	no trial data cached
Palmar-plantar erythrodysaesthesia syndrome	5	6.1 2.6–14.7ROR 6.2 · χ² 17 / p 2e-5	4.2 EB05 2.0 · IC025 +0.5	No label text to screen label has no adverse-reaction text	–	no trial data cached
Product substitution issue	11	5.5 3.1–9.9ROR 5.6 · χ² 36 / p 9e-10	4.6 EB05 2.7 · IC025 +1.2 3/3 methods agree	Reporting / coding artifact	serious PRR 9.3	no trial data cached

Trial evidence (ClinicalTrials.gov)

Trial cross-check not yet run for this drug (ClinicalTrials.gov pull covers the 800 most-reported drugs first).

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
Mouth ulceration	12	16.4 9.4–28.7ROR 16.7 · χ² 158 / p 1e-36	15.3 EB05 8.4 · IC025 +2.4 3/3 methods agree	No label text to screen label has no adverse-reaction text	serious PRR 11.9	no trial data cached
Product substitution issue	11	5.5 3.1–9.9ROR 5.6 · χ² 36 / p 9e-10	4.6 EB05 2.7 · IC025 +1.2 3/3 methods agree	Reporting / coding artifact	serious PRR 9.3	no trial data cached
Oral herpes	11	16.3 9.0–29.2ROR 16.5 · χ² 143 / p 3e-33	15.0 EB05 7.9 · IC025 +2.3 3/3 methods agree	No label text to screen label has no adverse-reaction text	serious PRR 7.6	no trial data cached
Oral pain	10	12.8 6.9–23.7ROR 13.0 · χ² 97 / p 3e-23	10.8 EB05 5.4 · IC025 +2.0 3/3 methods agree	No label text to screen label has no adverse-reaction text	serious PRR 12.8	no trial data cached
Tendonitis	7	12.9 6.2–27.0ROR 13.0 · χ² 66 / p 3e-16	9.9 EB05 4.3 · IC025 +1.5 3/3 methods agree	No label text to screen label has no adverse-reaction text	serious PRR 18.0	no trial data cached
Hair texture abnormal	7	14.9 7.1–31.2ROR 15.0 · χ² 77 / p 7e-19	12.0 EB05 5.0 · IC025 +1.6 3/3 methods agree	No label text to screen label has no adverse-reaction text	serious n=2	no trial data cached
Palmar-plantar erythrodysaesthesia syndrome	5	6.1 2.6–14.7ROR 6.2 · χ² 17 / p 2e-5	4.2 EB05 2.0 · IC025 +0.5	No label text to screen label has no adverse-reaction text	–	no trial data cached
Impaired driving ability	5	12.6 5.3–30.2ROR 12.7 · χ² 43 / p 3e-11	8.3 EB05 3.2 · IC025 +1.1 3/3 methods agree	No label text to screen label has no adverse-reaction text	serious PRR 18.4	no trial data cached
Gastrointestinal pain	5	13.1 5.5–31.4ROR 13.2 · χ² 45 / p 1e-11	8.8 EB05 3.3 · IC025 +1.1 3/3 methods agree	No label text to screen label has no adverse-reaction text	serious PRR 21.8	no trial data cached
Metrorrhagia	4	6.6 2.5–17.7ROR 6.7 · χ² 14 / p 9e-5	4.2 EB05 1.8 · IC025 +0.3	No label text to screen label has no adverse-reaction text	serious n=3	no trial data cached
Blood count abnormal	4	7.5 2.8–19.9ROR 7.5 · χ² 16 / p 3e-5	4.5 EB05 1.9 · IC025 +0.4	Lab value / disease marker	–	no trial data cached
Hair colour changes	4	9.1 3.4–24.3ROR 9.2 · χ² 21 / p 2e-6	5.3 EB05 2.1 · IC025 +0.5 3/3 methods agree	No label text to screen label has no adverse-reaction text	–	no trial data cached
Breast pain	4	10.8 4.1–28.7ROR 10.8 · χ² 26 / p 1e-7	6.3 EB05 2.4 · IC025 +0.6 3/3 methods agree	No label text to screen label has no adverse-reaction text	serious n=3	no trial data cached
Menorrhagia (heavy periods)	3	4.3 1.4–13.4ROR 4.3 · χ² 5 / p 0.015	2.9 EB05 1.2 · IC025 -0.5 PRR-only: not supported by EBGM or IC	No label text to screen label has no adverse-reaction text	serious PRR 10.6	no trial data cached
Amenorrhoea (missed periods)	3	5.2 1.7–16.0ROR 5.2 · χ² 6 / p 0.006	3.3 EB05 1.3 · IC025 -0.4 PRR-only: not supported by EBGM or IC	No label text to screen label has no adverse-reaction text	serious PRR 12.9	no trial data cached

Unlabeled candidate signals

Every screened signal with n ≥ 20 was either labeled, an indication term, or an artifact pattern — no unlabeled candidate stood out in the top signals.

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 L-Lysine?

In FDA FAERS, the most frequently co-reported reaction terms for L-Lysine are mouth ulceration, oral herpes, oral pain, tendonitis, hair texture abnormal, palmar-plantar erythrodysaesthesia syndrome. 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 L-Lysine have an FDA boxed warning?

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

Do FAERS signals prove that L-Lysine 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 0d46216b-bb97-4b10-8002-a93371f4bf24, effective 20260108; matched on openfda.generic_name.exact:"L-LYSINE")
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, 18 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

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.