Ketamine Therapy Side Effects

This is the honest clinical-safety profile of supervised ketamine therapy at therapeutic psychiatric doses. Most acute side effects are transient and resolve within 1–2 hours of dosing — mild nausea, brief blood pressure elevation, dizziness, headache, and the dissociative experience itself. Long-term concerns from chronic recreational ketamine misuse — bladder ulceration, hepatic and biliary toxicity, cognitive effects, dependency — have not generally emerged at therapeutic supervised doses. The largest published long-term safety data set (Wajs et al., SUSTAIN-2, J Clin Psychiatry 2020) followed 802 patients on Spravato + oral antidepressant for up to one year and reported no cases of interstitial cystitis. Murrough et al.'s 2015 safety analysis of repeated IV ketamine in TRD (J Clin Psychiatry) and the American Psychiatric Association Sanacora et al. 2017 consensus (JAMA Psychiatry) remain the standard references for the acute and short-term safety profile. This article covers what the evidence says, what to expect during and after a session, drug interactions, when to call your clinic urgently, and the meaningful distinction between therapeutic and recreational use. For the experiential / dissociation side specifically, see Does Ketamine Therapy Get You High? — this article focuses on clinical safety.

Key takeaways

• Acute side effects during/after a session: dissociation (intended therapeutic effect), brief blood pressure and heart rate elevation, mild nausea, dizziness, and headache. Most resolve within 1–2 hours of dosing.
• Long-term safety at therapeutic dose: SUSTAIN-2 (Wajs 2020) followed 802 patients on Spravato for up to a year and found no cases of interstitial cystitis. Bladder, hepatic, and dependency concerns from chronic recreational use have not generally emerged at therapeutic supervised doses.
• Drug interactions: high-dose benzodiazepines may attenuate ketamine's antidepressant effect; MAOIs are typically excluded; lamotrigine has weak signals of attenuation; SSRIs and SNRIs are generally compatible.
• Pre-treatment screening: cardiovascular evaluation (BP, HR, history; ECG for IV protocols), liver function for chronic dosing, substance use history, pregnancy, medication review.
• Red-flag symptoms after a session: persistent disorientation >2–3 hours, sustained hypertension, severe nausea, chest pain, severe headache, urinary symptoms, worsening mood or suicidal ideation. Contact the clinic urgently or go to the ER.
• The clinical-recreational distinction matters: therapeutic supervised ketamine has a fundamentally different safety profile than chronic recreational ketamine misuse.

What does the evidence say about ketamine safety?

The clinical safety literature for therapeutic psychiatric ketamine has grown substantially since the 2010s. Three references anchor most discussions:

Murrough et al. 2015 — Journal of Clinical Psychiatry — pooled safety analysis of 205 IV ketamine infusions in 97 patients with treatment-resistant depression. Conclusion: at sub-anaesthetic supervised doses, ketamine was "safe and well tolerated." Hemodynamic changes (transient BP and HR elevation) were the most common adverse event. No persistent psychotomimetic effects, no increased substance use at long-term follow-up. (PubMed)

Sanacora et al. 2017 — JAMA Psychiatry — American Psychiatric Association Council of Research consensus statement on the use of ketamine in the treatment of mood disorders. Establishes pre-treatment screening, dosing, monitoring, and post-treatment standards still widely referenced. (PubMed)

Wajs et al. 2020 — Journal of Clinical Psychiatry — SUSTAIN-2 long-term open-label safety study. 802 patients on intranasal esketamine (Spravato) + oral antidepressant for up to one year. Acceptable long-term safety profile; no cases of interstitial cystitis observed. (PubMed)

The honest framing: at therapeutic supervised doses, ketamine is generally well-tolerated with predominantly transient side effects. Most concerns about chronic ketamine harm derive from recreational misuse patterns at gram-level, frequent, unsupervised exposure — a profile fundamentally different from clinical practice.

Acute side effects — what to expect during and after a session

Dissociation

Dissociation — feeling temporarily disconnected from body, time, or surroundings — is the intended therapeutic experience of ketamine, not a side effect. It begins within 5–10 minutes of an IV infusion or IM injection, peaks at 20–30 minutes, and resolves over 30–60 minutes after dosing ends. Most patients describe it as floating, time distortion, emotional softening, and a sense of openness. Some experience it as profound; others as mild and unremarkable. For a deeper exploration of what dissociation feels like and why it matters therapeutically, see Does Ketamine Therapy Get You High?.

A small minority of patients find acute dissociation distressing rather than therapeutic. Preparation work, set and setting, clinician presence, and grounding techniques are the standard mitigations. A subsequent dose may be lowered.

Cardiovascular — transient BP and HR elevation

Ketamine acutely elevates sympathetic tone. Blood pressure and heart rate typically rise during the dosing window — often by 10–20% from baseline — and return to baseline within 1–2 hours. This is why pre-treatment cardiovascular screening matters and why blood pressure is monitored continuously during sessions. Uncontrolled severe hypertension is an absolute contraindication; well-controlled hypertension on appropriate medication is generally compatible.

Nausea and gastrointestinal

Mild nausea and occasional emesis occur in ~10–20% of sessions. Pre-treatment fasting (typically 4–6 hours) reduces incidence. Anti-emetics are available in clinic if needed.

Dizziness, blurred vision, and headache

Mild and transient. Most patients report these resolve within 1–2 hours of dosing.

Anxiety surge during dissociation

Some patients — particularly those with prominent baseline anxiety, dissociative trauma history, or insufficient preparation — experience an anxiety spike during peak dissociation. Trauma-trained therapists, eye shades, music, low first dose, and grounding techniques are standard mitigations.

Long-term safety — what the evidence supports and where caution remains

The honest framing of long-term safety: most concerns documented in the literature derive from chronic recreational ketamine misuse — gram-level, frequent, unsupervised use over months to years. SUSTAIN-2's one-year safety profile in 802 patients on Spravato + oral antidepressant remains the largest long-term therapeutic safety data set and is reassuring.

Bladder and ulcerative cystitis

Ketamine-associated ulcerative cystitis was first documented in case series of chronic recreational users. The pattern in those reports: gram-level daily use sustained over months. SUSTAIN-2 found no cases of interstitial cystitis at therapeutic Spravato dosing over up to one year. Murrough et al.'s analysis of repeated IV protocols similarly did not surface cystitis as a clinical issue at therapeutic doses.

The clinical implication: bladder symptoms are not an established concern at therapeutic supervised doses, but baseline urinalysis and ongoing monitoring for urinary symptoms are appropriate for chronic maintenance protocols. Patients should report any urinary changes.

Hepatic and biliary effects

Drug-induced liver injury and ketamine-associated cholangiopathy have been reported, particularly with multi-day infusion protocols in chronic pain populations and with chronic recreational use (Noppers et al., 2010, Pain). At psychiatric therapeutic doses, hepatic toxicity has not generally emerged, but baseline liver-function tests and ongoing monitoring are appropriate for repeated/maintenance dosing.

Cognitive effects

Acute cognitive effects (during dissociation) resolve along with dissociation itself. Long-term cognitive concerns from chronic recreational ketamine use have been reported but have not been replicated at therapeutic supervised doses. SUSTAIN-2's one-year follow-up did not surface persistent cognitive impairment as a clinical issue.

Dependence and misuse risk

Ketamine has misuse potential, particularly via recreational unsupervised use. In supervised in-clinic protocols at sub-anaesthetic doses with no take-home dispensing, dependence has not emerged as a clinical issue in published trials. History of ketamine misuse is a hard exclusion at most KAP clinics. The Janssen Journey program for Spravato explicitly forbids take-home dosing for this reason. For more, see Ketamine Therapy for Addiction.

Drug interactions

The honest summary: most psychiatric medications are compatible with ketamine therapy. The main concerns are MAOIs (excluded), high-dose benzodiazepines (may blunt effect), and active substance use disorder (separate exclusion).

Pre-treatment screening — what your intake will check

Comprehensive pre-treatment screening is part of safe ketamine therapy. The ATMA CENA intake call typically includes:

• Cardiovascular screening: blood pressure (both arms), heart rate, ECG (mandatory before IV protocols; often included for IM/SL/Spravato in patients with cardiovascular risk factors), history of cardiovascular disease, structural heart disease, recent MI (within ~6 weeks is exclusion), valvular disease, or aneurysm.
• Liver function: baseline AST, ALT, GGT particularly relevant for repeated/maintenance dosing.
• Urinalysis: baseline, particularly for patients with urinary symptoms history.
• Substance use history: ketamine misuse is a hard exclusion; other SUD history is reviewed for screening clarity.
• Pregnancy: pregnancy testing for women of reproductive age; pregnancy is an absolute contraindication.
• Medication review: MAOIs, high-dose benzodiazepines, lamotrigine, polypharmacy review.
• Psychiatric stabilization: active psychosis is an absolute contraindication; active mania or hypomania within 3 months is typically an exclusion; active suicidal ideation is reviewed with safety planning rather than excluded outright.

For the full eligibility framework, see How to Qualify for Ketamine Therapy in Canada.

What to monitor after a session — red-flag symptoms

Most patients leave the clinic feeling tired, somewhat raw or open, and possibly mildly dehydrated. The 24-hour no-driving rule is universal. The following symptoms warrant urgent contact with your clinic — or, if severe or after-hours, with emergency services:

• Persistent disorientation or confusion lasting more than 2–3 hours after session end.
• Sustained elevated blood pressure (e.g., ≥160/100 mmHg) not resolving within 1 hour of discharge.
• Severe nausea or vomiting preventing oral intake or lasting more than 3 hours.
• Chest pain, shortness of breath, or palpitations.
• Severe headache not controlled by rest, hydration, or routine analgesia.
• Urinary symptoms — blood in urine, painful urination, inability to urinate. Rare but should be reported, particularly during maintenance protocols.
• Worsening mood, severe anxiety surge, or suicidal ideation in the 24–72 hours after session.
• Persistent inability to coordinate movements or sustained dizziness lasting more than 4 hours.
• Fever, chills, or signs of infection at the IV site (for IV protocols).

For acute psychiatric crisis, please call 9-8-8 (Canada Suicide Crisis Helpline) or go to your nearest emergency department.

The clinical-recreational distinction — honest framing

Therapeutic supervised ketamine has a fundamentally different safety profile than recreational ketamine misuse. Here is the honest comparison:

The bladder, hepatic, cognitive, and dependence concerns documented in the recreational misuse literature have not generally emerged at therapeutic supervised doses. SUSTAIN-2's 802-patient one-year safety profile is the most direct counter-example to those concerns at clinical dosing.

This is not to minimize legitimate caution — long-term maintenance therapy at supervised therapeutic dose has limited multi-year data, and clinical screening, monitoring, and informed consent matter. It is to frame the discussion honestly.

Frequently asked questions

Is ketamine therapy safe? At sub-anaesthetic supervised doses with appropriate pre-treatment screening, ketamine has a well-characterized short-term safety profile (Murrough 2015) and acceptable long-term safety up to one year (Wajs 2020 SUSTAIN-2). Most adverse events are transient and resolve within 1–2 hours of dosing.

What are the most common side effects? Brief blood pressure and heart rate elevation, mild nausea, dizziness, headache, and the dissociative experience itself. Most resolve within 1–2 hours of dosing.

Can ketamine therapy damage my bladder? Bladder/cystitis concerns documented in recreational misuse case series have not emerged at therapeutic supervised doses. SUSTAIN-2 (802 patients on Spravato up to a year) found no cases of interstitial cystitis. Maintenance protocols include monitoring for urinary symptoms.

Can ketamine therapy damage my liver? Hepatotoxicity has been reported with multi-day infusion protocols in chronic pain (Noppers 2010) and with chronic recreational use. At psychiatric therapeutic doses, hepatic toxicity has not generally emerged. Baseline and ongoing liver-function monitoring are appropriate for repeated/maintenance dosing.

Will I become dependent on ketamine? At supervised in-clinic doses with no take-home dispensing, dependence has not emerged as a clinical issue in published trials. Ketamine has misuse potential via unsupervised recreational use; the Janssen Journey program for Spravato explicitly prohibits take-home dosing for this reason.

What about my benzodiazepine prescription? High-dose benzodiazepines may attenuate ketamine's antidepressant effect. This is rarely a hard exclusion but is a meaningful consideration; our clinical team will discuss timing or tapering with you and your prescriber where appropriate.

Can I keep taking my SSRI? Generally yes. Most pivotal Spravato trials (Daly 2018, Popova 2019) tested esketamine + oral antidepressant combination. Continue your antidepressant unless your prescriber has a specific reason to taper.

Is dissociation dangerous? Dissociation is the intended therapeutic experience, not a side effect. It is transient (resolves in 30–60 minutes after dosing ends) and managed by clinician presence, set/setting, and grounding techniques. Patients with severe baseline dissociative symptoms (e.g., depersonalization/derealization disorder, complex trauma) may find dissociation distressing — this is screened during intake.

What should I tell my clinic if I notice something after the session? Use the red-flag list above. Most post-session symptoms resolve within hours; persistent disorientation, sustained hypertension, chest pain, severe headache, urinary symptoms, or worsening mood warrant urgent clinic contact. For psychiatric crisis, call 9-8-8 or go to your nearest emergency department.

Are the side effects worse with IV than IM or sublingual? Acute side effects (BP elevation, dissociation) tend to be more pronounced with IV due to higher peak plasma levels. IM has similar peaks; SL is milder due to lower bioavailability (~30%). Spravato's profile is between IV and SL for most patients. The clinical setting and monitoring rigor are tuned to the route used.

Are the side effects different with Spravato? Spravato's most common acute effects are dissociation, dizziness, sedation, nausea, and blood pressure elevation. Mandatory ≥2-hour post-dose observation is part of the Janssen Journey requirement. SUSTAIN-2 long-term safety (Wajs 2020) is the largest published long-term data set and is the standard reference.

Sources

1. Murrough JW, et al. (2015). Ketamine safety and tolerability in clinical trials for treatment-resistant depression. J Clin Psychiatry. https://pubmed.ncbi.nlm.nih.gov/25749511/
2. Sanacora G, Frye MA, McDonald W, et al. (2017). A consensus statement on the use of ketamine in the treatment of mood disorders. JAMA Psychiatry. https://pubmed.ncbi.nlm.nih.gov/28249076/
3. Wajs E, et al. (2020). Esketamine nasal spray plus oral antidepressant in TRD: SUSTAIN-2 long-term safety. J Clin Psychiatry. https://pubmed.ncbi.nlm.nih.gov/32316080/
4. Noppers IM, et al. (2010). Drug-induced liver injury following a repeated course of ketamine treatment for chronic pain. Pain. https://pubmed.ncbi.nlm.nih.gov/20705391/
5. Andrashko V, et al. (2020). The antidepressant effect of ketamine is dampened by concomitant benzodiazepine medication. Front Psychiatry. https://pubmed.ncbi.nlm.nih.gov/33384625/
6. Daly EJ, et al. (2018). Phase 2 dose-response esketamine in TRD. JAMA Psychiatry. https://pubmed.ncbi.nlm.nih.gov/29282469/
7. Popova V, et al. (2019). TRANSFORM-2 — esketamine + new oral antidepressant in TRD. Am J Psychiatry. https://pubmed.ncbi.nlm.nih.gov/31109201/
8. Swainson J, et al. (2021). CANMAT racemic ketamine task force recommendations. Can J Psychiatry. https://pubmed.ncbi.nlm.nih.gov/33174760/
9. Health Canada — Product InfoWatch (March 2022, ketamine): https://www.canada.ca/en/health-canada/services/drugs-health-products/medeffect-canada/health-product-infowatch/march-2022.html
10. CPSA — Ketamine Clinical Toolkit: https://cpsa.ca/resources/ketamine-toolkit/
11. Government of Canada — 9-8-8 Suicide Crisis Helpline: https://988.ca/

Related articles in this cluster

• Ketamine Therapy in Canada
• What Is Ketamine Therapy?
• Does Ketamine Therapy Get You High? — experiential framing of dissociation
• How to Qualify for Ketamine Therapy in Canada
• Ketamine Infusion Therapy
• Intravenous Ketamine Therapy
• Intranasal Ketamine and Spravato
• Group Ketamine Therapy
• Ketamine Therapy for Addiction
• Insurance Coverage for Ketamine Therapy

Last updated: 2026-05-06