Ketamine in Pregnancy and Lactation: Safety Considerations and Data Gaps

Introduction: The Clinical Dilemma

The safety of ketamine in pregnancy and lactation represents a critically important but inadequately studied area with direct implications for the management of treatment-resistant depression and acute suicidality in pregnant and postpartum individuals. Ketamine safety considerations during pregnancy and lactation are complicated by the convergence of three factors: the severity and urgency of the conditions for which ketamine is prescribed -- see our contraindications and screening overview --, the ethical and practical constraints on conducting clinical trials in pregnant populations, and the concerning preclinical evidence regarding NMDA receptor blockade during neurodevelopment (Bhutta, 2007). The result is a clinical landscape characterized by significant data gaps that clinicians must navigate when managing severely depressed or suicidal pregnant and postpartum patients.

Perinatal depression affects approximately 10-20% of pregnant individuals, with treatment-resistant forms representing a significant proportion (Gaynes et al., 2005). The consequences of untreated severe depression during pregnancy -- including suicidal behavior (a leading cause of maternal mortality), poor prenatal care adherence, preterm delivery, low birth weight, and impaired maternal-infant bonding -- are well-documented and can be devastating. When conventional treatments fail, the question of whether ketamine can be safely considered during pregnancy represents a genuine clinical dilemma without clear answers. For a discussion of the broader clinical framework, see patient selection criteria.

Preclinical Developmental Toxicity Data

Apoptotic Neurodegeneration in Developing Brain

The most concerning preclinical finding is the demonstration that NMDA receptor antagonism during the brain growth spurt period triggers widespread apoptotic neurodegeneration in the developing brain. Ikonomidou and colleagues (1999), in a landmark study published in Science, showed that a single dose of the NMDA antagonist MK-801 produced massive neuronal apoptosis in the neonatal rat brain, with affected regions including the hippocampus, thalamus, and cortex. Subsequent studies confirmed that ketamine specifically produces similar neurodegenerative effects in developing rodent and non-human primate brains.

Brambrink and colleagues (2012) demonstrated that a five-hour ketamine infusion (maintaining anesthetic-level plasma concentrations) in neonatal rhesus macaques produced significantly increased neuronal apoptosis throughout the cerebral cortex. Follow-up studies revealed long-term behavioral consequences, including impaired learning, memory deficits, and altered social behavior in exposed animals (Paule et al., 2011). These findings led to the FDA's 2016 Drug Safety Communication warning about the potential neurodevelopmental effects of anesthetic agents, including ketamine, in children under three years and during the third trimester of pregnancy.

Critical Developmental Window

The vulnerable period for NMDA receptor blockade-induced neurotoxicity corresponds to the brain growth spurt -- a period of rapid synaptogenesis during which NMDA receptors play critical roles in neuronal survival, migration, and circuit formation -- mechanisms central to neuroplasticity. In rodents, this period spans approximately postnatal days 1-14. In humans, the corresponding period extends from approximately the third trimester of pregnancy through the first two years of postnatal life, with peak vulnerability in the late prenatal and early postnatal period (Bhutta, 2007).

First-trimester exposure -- when organogenesis occurs but before the brain growth spurt -- may carry different risks, potentially involving structural malformations rather than neuroapoptosis. Conventional animal teratogenicity studies of ketamine (examining structural malformations rather than neuroapoptosis) have generally not demonstrated increased rates of major structural malformations at clinically relevant doses, though some studies in mice have reported minor skeletal variations at high doses (Brindle et al., 1987).

Dose-Response and Exposure Duration Considerations

The preclinical neurotoxicity data must be interpreted in the context of dose and exposure duration. The studies demonstrating significant neuroapoptosis employed anesthetic doses maintained for hours -- conditions vastly different from a single 40-minute sub-anesthetic infusion. Whether brief, sub-anesthetic exposure during the vulnerable period poses a meaningful neurodevelopmental risk remains unknown but is biologically plausible at some threshold. The pharmacokinetic principles of transplacental drug transfer suggest that fetal exposure following a maternal 0.5 mg/kg IV ketamine infusion would be substantially lower than the anesthetic concentrations used in preclinical studies (Ngan Kee et al., 2014).

Human Data: Limited Evidence

Case Reports and Case Series

Published human data on ketamine exposure during pregnancy consist primarily of case reports and small retrospective series, predominantly describing anesthetic use during cesarean delivery or procedural sedation rather than repeated sub-anesthetic psychiatric use. Stutsman and colleagues (2010) described a case of chronic recreational ketamine use during pregnancy resulting in normal neonatal outcomes at delivery, though long-term developmental follow-up was not reported.

Li and colleagues (2017) reported on neonatal outcomes following maternal ketamine use for anesthesia during cesarean delivery in a retrospective cohort, finding no increased rate of adverse neonatal outcomes (Apgar scores, neonatal intensive care admission) compared with non-ketamine anesthesia. However, this study assessed only immediate neonatal outcomes and did not include neurodevelopmental follow-up.

Registry Data

No prospective pregnancy registry exists specifically for ketamine or esketamine exposure. The esketamine (Spravato) prescribing information recommends pregnancy testing prior to initiating therapy and advises against use during pregnancy based on the preclinical neurodevelopmental data. A pregnancy registry has been established for esketamine, but enrollment numbers and outcome data have not yet been published in sufficient detail to draw conclusions (Janssen Pharmaceuticals, 2019).

Epidemiological Studies

Large-scale epidemiological studies of ketamine exposure during pregnancy are absent from the literature. The International Registry of Antiepileptic Drugs and Pregnancy (EURAP) provides a model for how such surveillance could be implemented, but no equivalent registry exists for ketamine psychiatric use during pregnancy.

Placental Transfer and Fetal Pharmacology

Transplacental Drug Passage

Ketamine crosses the placenta readily due to its lipophilicity, low molecular weight (237.7 Da), and moderate protein binding (approximately 47%). The fetal-to-maternal plasma concentration ratio reaches approximately 0.7-1.0 at steady state during continuous maternal infusion, indicating substantial fetal exposure (Ngan Kee et al., 2014). Following a single maternal infusion, fetal plasma concentrations follow the maternal kinetic profile with a brief lag, reaching peak levels within minutes of peak maternal concentrations.

Ketamine metabolism in the fetus is limited by the immaturity of hepatic cytochrome P450 enzymes, potentially resulting in longer fetal half-life and greater cumulative exposure relative to the mother. The active metabolite norketamine also crosses the placenta and accumulates in fetal circulation, adding to the total NMDA receptor-antagonist exposure.

Amniotic Fluid Accumulation

Ketamine and its metabolites have been detected in amniotic fluid following maternal administration, suggesting the potential for fetal exposure beyond direct transplacental transfer through fetal swallowing of amniotic fluid. The clinical significance of amniotic fluid drug accumulation in the context of single-dose or intermittent exposure is uncertain.

Lactation Considerations

Breast Milk Transfer

Limited data exist on ketamine transfer into human breast milk. Marchetti and colleagues (2022), published in Breastfeeding Medicine, measured ketamine and norketamine concentrations in breast milk following a single intravenous infusion of ketamine (0.5 mg/kg) in four postpartum women. Ketamine was detectable in breast milk at peak concentrations of approximately 100-200 ng/mL, with a milk-to-plasma ratio of approximately 0.5-0.8. Norketamine concentrations in milk were comparable to or exceeded parent drug levels.

Infant Exposure Estimates

Based on available pharmacokinetic data, the estimated infant dose via breast milk following a single maternal ketamine infusion is approximately 0.5-3% of the weight-adjusted maternal dose -- a relative infant dose (RID) below the generally accepted safety threshold of 10%. However, this estimate applies to single-dose exposure and does not account for the potential effects of repeated maternal dosing on cumulative infant exposure.

Recommendations for Breastfeeding

Given the limited data, pragmatic recommendations for breastfeeding during ketamine therapy include:

• Single infusions: Pump and discard breast milk for 12-24 hours following infusion (covering approximately 4-8 half-lives of ketamine and norketamine elimination), then resume breastfeeding. This approach effectively eliminates meaningful infant exposure from individual sessions.
• Repeated infusions: The pump-and-discard strategy can be applied to each infusion session, though the practical burden increases with treatment frequency. For patients receiving twice-weekly infusions, the cumulative burden of milk discarding may be impractical and may necessitate supplemental formula feeding during active treatment periods.
• Oral/sublingual ketamine: Daily or frequent oral ketamine administration during lactation is more concerning due to sustained maternal drug levels and continuous infant exposure. The safety of this exposure pattern has not been studied, and caution is warranted.

Risk-Benefit Framework for Clinical Decision-Making

Severity-Based Approach

Clinical decision-making regarding ketamine during pregnancy should be guided by a severity-based framework that weighs the risks of ketamine exposure against the risks of untreated or inadequately treated maternal psychiatric illness:

Mild-moderate depression: Ketamine exposure is not justified. First-line treatments (SSRIs, psychotherapy) with established pregnancy safety profiles should be optimized.

Severe treatment-resistant depression without imminent risk: Ketamine should be considered only after exhaustive trials of safer alternatives, including multiple antidepressant classes, psychotherapy modalities, and ECT (which has an established safety record in pregnancy). If ketamine is considered, limiting exposure to the minimum effective number of infusions and avoiding first-trimester and third-trimester exposure when possible is advisable.

Acute suicidal crisis with imminent risk: In life-threatening situations, the acute risk of maternal suicide may outweigh the theoretical developmental risks of a single ketamine infusion. Emergency ketamine administration for imminent suicidality in a pregnant patient represents a clinical scenario in which the immediate threat to maternal life takes precedence, analogous to the use of potentially teratogenic medications (anticonvulsants, antipsychotics) when the alternative is catastrophic.

Electroconvulsive Therapy as Comparator

ECT has a substantially larger safety database in pregnancy than ketamine, with case series and retrospective studies spanning several decades. While not without risk (uterine contractions, transient fetal heart rate changes), ECT is generally considered safe during pregnancy when administered with appropriate obstetric monitoring (Anderson and Reti, 2009). For pregnant patients with severe treatment-resistant depression, ECT represents the evidence-based alternative with the most established safety record and should be preferentially considered before ketamine.

Consent and Counseling

Essential Elements of Informed Consent

If ketamine is considered during pregnancy, the informed consent process must explicitly address:

• The absence of established safety data for sub-anesthetic ketamine in human pregnancy
• The preclinical evidence of NMDA receptor blockade-induced neurodevelopmental toxicity at high doses
• The uncertainty about whether sub-anesthetic, brief exposure translates to meaningful human developmental risk
• Available alternatives and their respective risk-benefit profiles
• The plan for maternal and fetal monitoring during and after treatment
• The patient's right to decline treatment without penalty

Shared Decision-Making

The complexity and uncertainty of this clinical scenario mandates a shared decision-making approach involving the patient, psychiatrist, obstetrician, and, when relevant, neonatologist. Documentation of the clinical reasoning, the alternatives considered, and the patient's informed decision is essential from both clinical and medicolegal perspectives.

Future Research Priorities

The most pressing research needs include prospective registries for ketamine/esketamine exposure during pregnancy, long-term neurodevelopmental follow-up of exposed children, pharmacokinetic modeling of fetal exposure at sub-anesthetic doses, breast milk kinetics during repeated dosing, and development of evidence-based guidelines through expert consensus. Animal studies examining neurodevelopmental outcomes following brief, sub-anesthetic ketamine exposure during the equivalent of human third-trimester development would also be highly informative.

Conclusion

Ketamine safety during pregnancy and lactation remains characterized by significant data gaps that preclude evidence-based guidelines. Preclinical neurodevelopmental toxicity data raise legitimate concerns, but the dose-exposure discrepancy between animal studies and clinical sub-anesthetic use limits direct extrapolation. Human data are confined to case reports and short-term outcome assessments without neurodevelopmental follow-up. A severity-based clinical framework -- reserving ketamine for life-threatening situations when safer alternatives have failed -- provides the most defensible approach given current knowledge. Prospective registries, long-term outcome surveillance, and dedicated pharmacokinetic studies represent essential research priorities for informing future clinical practice in this challenging area.

References

• FDA MedWatch: Safety Information and Adverse Event Reporting — FDA safety reporting system for pregnancy-related drug adverse events
• MedlinePlus: Ketamine Injection Drug Information — National Library of Medicine medication information including pregnancy category warnings
• AAP: American Academy of Pediatrics — Professional society providing guidance on medication use during lactation and neonatal drug exposure
• DailyMed: FDA Drug Label Information — National Library of Medicine database for official drug labeling including pregnancy and lactation sections