Ibogaine QTc Study: Heart Effects in 14 Patients (2021)

Quick answer

In Knuijver's 2021 study, a single oral dose of ibogaine (10 mg/kg) lengthened the heart's QTc interval by about 95 ms on average in 14 opioid-dependent patients, and half went above 500 ms. All of them had severe temporary ataxia. Nobody developed torsades, but with only 14 people that doesn't show the drug is safe. Ibogaine is Schedule I and not approved.

Definition

Definition: Knuijver et al. (2021) in *Addiction* (doi: 10.1111/add.15448; PMID 33620733) is a descriptive open-label observational safety study of a single oral ibogaine HCl 10 mg/kg dose in n=14 opioid-dependent patients in a Dutch university medical center after conversion to morphine sulfate. Mean maximum QTc (Fridericia) prolongation was about +95 ms (range ~29–146 ms); 50% of subjects reached QTc >500 ms; severe transient ataxia occurred in all; no torsades de pointes were observed in this small sample. This is critical cardiac teaching—and not proof of physician-supervised IV ibogaine infusion (psychoactive intravenous ibogaine). Absence of TdP in n=14 does not equal cardiac safety. Ibogaine is U.S. Schedule I and not approved for any indication.

Short answer

Knuijver and colleagues’ 2021 Addiction study gave oral ibogaine 10 mg/kg to 14 opioid-dependent patients and found mean QTc prolongation near 95 milliseconds, with half exceeding 500 milliseconds, plus severe ataxia. No torsades occurred in that small sample, yet risk remains serious. This oral safety study does not prove psychoactive IV ibogaine infusion.

Why this paper matters

Knuijver 2021 is among the clearest monitored university measurements of oral ibogaine’s acute cardiac and cerebellar effects. Clinics sometimes misuse “no TdP observed” as a green light. This page keeps magnitudes, percentages, and route labels intact. Related: /blog/ibogaine-mortality-cardiac-risk · /safety-and-screening · /blog/ibogaine-ecg-pre-infusion-checklist.

What was studied

Methods (plain language)

Patients hoping for abstinence after unsuccessful standard care were converted to morphine, then given one weight-based oral ibogaine dose in hospital. Staff repeatedly measured heart rhythm intervals (QTc), vital signs, walking/coordination (ataxia), and psychoactive/delirium-observation scores for at least a day. The study’s purpose was safety description, not a pivotal efficacy RCT.

Other acute effects are covered in ibogaine side effects: nausea, ataxia and heart risk.

Key findings (no hype)

As reported:

• Mean maximum QTcF prolongation ≈ 95 ms (range about 29–146 ms).
• 50% of subjects reached QTc >500 ms during observation.
• In 6/14, QTc prolongation above 450 ms lasted beyond 24 hours.
• No TdP observed in this sample.
• Bradycardia / BP decreases noted.
• Severe transient ataxia with inability to walk without support in all patients.
• Withdrawal/psychomimetic effects mostly manageable in the 24-hour window (11/14 did not return to morphine within 24 h; DOS remained below threshold as reported).

Honest reading: large QTc shifts in a supervised hospital sample are a warning, not a marketing footnote. “No TdP here” is underpowered reassurance.

Limits and confounders

Later PK/PD work linked to this cohort (Knuijver et al., *J Psychopharmacol* 2024; doi 10.1177/02698811241237873) further discusses CYP2D6-related clearance variability and exposure–response ideas—covered separately at /blog/knuijver-2024-ibogaine-pk-cyp2d6, not invented here as IV proof.

Route honesty: oral ≠ psychoactive IV

Knuijver dosed oral ibogaine HCl. Pharmacokinetics, peak timing, and acute ataxia patterns may differ from intravenous psychoactive delivery. Regardless, QTc biology is not a loophole: IV ibogaine infusion still requires physician supervision, ECG screening, electrolytes, and continuous monitoring culture. Support IV magnesium ≠ proof that oral QTc data are irrelevant (/blog/magnesium-ibogaine-cardiac-protocol, /blog/ibogaine-oral-vs-iv).

Cardiac safety context

QTc >500 ms is a conventional red-flag threshold for TdP risk discussions. A study where half of subjects cross that line after a single oral dose is foundational health content for any ibogaine webpage. Pair with mortality synthesis (/blog/ibogaine-mortality-cardiac-risk), telemetry/ACLS expectations (/blog/ibogaine-telemetry-acls-monitoring), and contraindications (/blog/ibogaine-contraindications, /blog/ibogaine-pre-existing-heart-conditions).

What this does NOT prove for IV ibogaine infusion

U.S. Schedule I / not approved. Treatment at our Mexico and Gabon intake locations ≠ approved U.S. clinic (/blog/is-ibogaine-legal-us).

How to interpret “no TdP observed” without false reassurance

Torsades de pointes is uncommon even among drugs that prolong QTc; a 14-person sample can easily miss it. Responsible interpretation:

1. Magnitude matters: mean ~+95 ms is large by clinical pharmacology standards.
2. Threshold crossings matter: half above 500 ms is a population red flag, not a trivia fact.
3. Duration matters: prolongation past 24 hours in 6/14 extends the risk window beyond a short “ceremony night” mindset.
4. Ataxia compounds risk: immobility, falls, and aspiration risk stack onto arrhythmia risk.
5. Setting matters: university telemetry ≠ understaffed retreat bedrooms.

Families comparing clinics should ask for continuous ECG/telemetry plans in writing (/blog/ibogaine-telemetry-acls-monitoring, /blog/cheap-ibogaine-clinic-red-flags).

Relationship to other paper summaries in this batch

Do not treat any single optimistic outcome paper as a rebuttal of Knuijver’s measurements.

Next steps

If Knuijver numbers prompted fear or curiosity about physician-supervised IV ibogaine infusion, do not DIY and do not bargain-hunt unmonitored retreats. Start at /safety-and-screening, then /apply only after cardiac education. Mortality article: /blog/ibogaine-mortality-cardiac-risk.

FAQ

What is Knuijver 2021? An open-label university safety study of oral ibogaine 10 mg/kg in 14 OUD patients focusing on QTc, vitals, ataxia, and acute effects.

How much did QTc rise? Mean maximum prolongation about +95 ms; half of participants exceeded 500 ms.

Did anyone have torsades in the study? No TdP was observed in this n=14 sample—insufficient to declare cardiac safety.

Was the dose intravenous? No. Oral ibogaine HCl.

Why did everyone have ataxia? Severe transient cerebellar/ataxic effects were observed in all participants—mobility support matters.

Does this prove IV ibogaine infusion is safe or effective? No. It is oral safety description, not an IV efficacy RCT.

Should I still get screening? Yes—non-negotiable (/safety-and-screening).

Is ibogaine approved for medical use? No. Schedule I in the U.S.; not approved for any indication.

Medical disclaimer

Educational research synopsis only—not medical, psychiatric, or legal advice, and not a guarantee of outcomes. Ibogaine can prolong the QTc interval and has been associated with serious cardiac events including torsades de pointes and death in some contexts. Ibogaine is Schedule I in the United States and is not approved for any indication. Our IV ibogaine programs in Mexico and Gabon are not approved U.S. clinics. Next steps: /safety-and-screening, then /apply.

Knuijver 2021 is oral QTc/ataxia safety literature—not psychoactive IV ibogaine proof.

Sources (selected)

1. Knuijver T., Schellekens A., Belgers M., et al. Safety of ibogaine administration in detoxification of opioid-dependent individuals: a descriptive open-label observational study. *Addiction*. 2021. doi: 10.1111/add.15448. PMID: 33620733.
2. Glue P. et al. *Clin Pharmacol Drug Dev*. 2016. doi: 10.1002/cpdd.254. (Oral noribogaine QTc.)
3. Köck P. et al. *J Subst Abuse Treat*. 2022. doi: 10.1016/j.jsat.2021.108717.
4. Mosca A. et al. *Curr Neuropharmacol*. 2023. doi: 10.2174/1570159X21666221017085612.
5. 21 CFR 1308.11 — ibogaine Schedule I (United States).

How much does ibogaine prolong QTc?

In this study, mean maximum QTc prolongation (Fridericia correction) was about +95 ms, ranging from about 29 to 146 ms between patients. Half of the 14 participants reached a QTc above 500 ms. That threshold is widely treated as a level of serious concern for arrhythmia risk. These patients were screened, in a university hospital, and monitored continuously.

Why does a QTc over 500 ms matter?

A long QTc means the heart takes longer to electrically reset between beats. That creates the conditions for ventricular arrhythmias such as torsades de pointes, which can be fatal. The mechanism, hERG potassium-channel blockade, is explained in our ibogaine heart-risk review.

Did anyone have a dangerous arrhythmia?

No torsades de pointes occurred in this sample. But 14 people is far too few to rule out a rare, serious event. Absence of torsades in n=14 is not evidence of cardiac safety, and the authors' findings argue for close monitoring.

How long did QTc stay prolonged?

Cardiac effects can persist while noribogaine, ibogaine's longer-lasting active metabolite, remains in the body. That is why monitoring should not stop when the acute experience ends. Ask any program how long telemetry continues after dosing.

What other side effects did patients have?

All 14 had severe, transient ataxia, meaning loss of coordination. That matters for fall risk and staffing. For the wider list, see ibogaine side effects.

Who was in the study?

Opioid-dependent adults treated in a Dutch university medical center, after being switched to morphine sulfate. It was open-label and observational, with no control group. It measured safety and pharmacology, not long-term recovery.

Does this apply to IV ibogaine?

Not directly. The dose was oral. Intravenous delivery changes the kinetics but does not remove ibogaine's effect on heart rhythm. On this site, IV ibogaine infusion means physician-supervised psychoactive IV dosing with continuous cardiac monitoring.

What should screening look like after reading this?

• A baseline ECG with a written QTc exclusion threshold.
• Potassium and magnesium checked and corrected.
• A full medication review for QT-prolonging and CYP2D6-interacting drugs (see ibogaine drug interactions).
• Continuous telemetry, serial ECGs, ACLS-trained staff and a defibrillator.

Program length depends on that screening; see how long ibogaine treatment takes. Programs serving U.S. patients operate abroad, with intake locations including Mexico and Gabon, and should meet the same standard.

Next step: Read safety and screening (/safety-and-screening), then apply (/apply).