Quinidine

A Class IA antiarrhythmic, FDA-approved for atrial fibrillation or flutter, ventricular arrhythmias and life-threatening falciparum malaria.

psilodex.org/m/quinidine · data v2026.10.05

Clinical contraindication: None listed; No label contraindication covering psilocybin was found. This is not a finding that the combination has been shown to be without risk.
Psilocybin evidence: No psilocybin data
Half-life: 6–8 h; Approximate, in adults. Source under Interaction below.

Named in state rules?

Not namedColorado Condition rules (3)

Not namedOregon

PendingNew Mexico

Cite asPsilodex, “Quinidine”, v2026.10.05. psilodex.org/m/quinidine

Clinical data and state rules are separate facts. Both are shown; neither is a decision.

What it is used for

FDA status

FDA-approved

FDA-approved for

Conversion of atrial fibrillation or flutter to normal rhythm
Reducing relapse into atrial fibrillation or flutter
Suppression of recurrent ventricular arrhythmias
Life-threatening Plasmodium falciparum malaria

Sources [1]

Other safety

The label reports that mortality with quinidine for atrial fibrillation or flutter was more than three times that of controls in a meta-analysis of trials.

About the medication itself, separate from any interaction with psilocybin.

Sources [1]

01 Interaction with psilocybin

Not studied with psilocybin; it blocks an enzyme that helps break down psilocybin, so higher levels are possible. Also, it can cause heart-rhythm (QT) effects.

Detail Quinidine prolongs the QT interval (a heart-rhythm measure) and has anticholinergic (drying, confusing) activity. Psilocybin transiently raises heart rate and blood pressure. At therapeutic levels, quinidine inhibits CYP2D6, an enzyme that metabolized nearly all psilocin (psilocybin's active form) in lab studies (Thomann 2024). So it may raise psilocin levels. However, the body clears psilocin mainly by glucuronidation and conversion to 4-HIAA. No psilocybin data exist. Sources [1][2]

Human data with psilocybin: No psilocybin data; based on how it works and its label
Half-life: 6–8 h (adults) (FDA label, checked 2026-10-04) Active metabolite 3-hydroxyquinidine ~12 h.

Evidence types on this record

No psilocybin dataNo psilocybin data: no human data with psilocybin or another classic psychedelic; the text draws on the medication's own pharmacology and its label or reference facts

02 Pharmacology relevant to psilocybin

2 listed · counted on reports

Anticholinergic: Blocks acetylcholine. Can cause a fast heart rate, dry mouth, reduced sweating and heat intolerance, and confusion, more so at high doses or in combination. Sources [1]
QT-prolonging: Lengthens the QT interval on an ECG, a measure of the heart’s electrical recovery between beats. A long QT raises the risk of a dangerous heart rhythm, more so with other QT-prolonging drugs or low potassium or magnesium. Sources [1]

03 State rules

Plain-language summary · official text governs

CO4 CCR 755-1

Not namedCondition rules (3)

No provision names this medication or its class.

Colorado · checked 2026-10-04

OROAR 333-333

Not named

No provision names this medication or its class.

Oregon · checked 2026-10-04

NM7.35.3 NMAC (proposed)

Pending

New Mexico's clinical rules (proposed 7.35.3 NMAC) are not final. No provision naming this medication has been found.

New Mexico · checked 2026-10-04

04 Conditions to ask about

Screening items in state rules

This medication is usually taken for a condition. State rules screen for some conditions directly, so the medication is a prompt to ask about them. Confirm with the participant; never assume a condition from the medication.

Cardiovascular disease likely
- CO 2.5(A)(2) · Clinical Facilitator licensees
- CO 6.16(F)(2)(a) · Facilitators without a clinical facilitator license
- CO 6.16(F)(1) · All licensees

05 Sources

Quinidine sulfate tablets (Epic Pharma) · FDA label (DailyMed) — revised 2023-12 | QT-prolonging: Warnings, Proarrhythmic Effects "Like many other drugs (including all other class IA antiarrhythmics), quinidine prolongs the QTC interval, and this can lead to torsades de pointes, a life-threatening ventricular arrhythmia" | Anticholinergic: Contraindications "Quinidine is also contraindicated in patients who, like those with myasthenia gravis, might be adversely affected by an anticholinergic agent." | "Quinidine is not metabolized by cytochrome P450IID6, but therapeutic serum levels of quinidine inhibit the action of cytochrome P450IID6, effectively converting extensive metabolizers into poor metabolizers." | "The elimination half-life is 6 to 8 hours in adults and 3 to 4 hours in children."
Thomann J, Kolaczynska KE, Stoeckmann OV, et al. In vitro and in vivo metabolism of psilocybin’s active metabolite psilocin. Front Pharmacol 2024;15:1391689. — Abstract: "recombinant CYP2D6 and CYP3A4 enzymes metabolized nearly 100% and 40% of psilocin, respectively." "MAO-A transformed psilocin into minimal amounts of 4-HIAA and 4-HTP." "In conclusion, MAO-A, CYP2D6, and CYP3A4 are involved in psilocin's metabolism." Introduction: "Around 33% of a psilocybin dose is renally excreted as 4-HIAA."

Record history

v2026.10.02First published.
2026-10-04Last reviewed against its sources.

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