How Ketamine Works in the Body: From Infusion to Brain Changes

Ketamine has been FDA-approved as an anesthetic since 1970, yet for most of its clinical life, its effects on the mind were considered a side effect to minimize. The past two decades of research have inverted that understanding entirely. What the brain does under the influence of sub-anesthetic ketamine doses, the very effects once classified as unwanted, turns out to be the mechanism of therapeutic action. At Soft Reboot Wellness in Menlo Park, understanding this pharmacology is not an academic exercise. It shapes how we dose, how we time infusions, and how we structure the integration work that follows.

The Moment of Infusion

When ketamine enters the bloodstream via IV, the delivery method used at Soft Reboot Wellness, it reaches peak plasma concentration quickly and crosses the blood-brain barrier efficiently. Within minutes of infusion onset, the drug begins binding to NMDA receptors: N-methyl-D-aspartate receptors that sit on the surface of neurons and play a central role in regulating how those neurons communicate.

NMDA receptors are part of the glutamate system (the brain’s primary excitatory neurotransmitter network), responsible for the majority of signaling between neurons (National Institutes of Health). Under normal circumstances, NMDA receptors open in response to glutamate binding and allow ions to flow across the neuron membrane, initiating electrical signals. Ketamine enters the receptor channel and blocks this flow. The receptor is occupied but not activated.

This blockade sounds suppressive, and in one narrow sense it is. But the downstream consequence is counterintuitive: blocking NMDA receptors transiently causes a compensatory surge of glutamate release in surrounding circuits. That surplus glutamate then activates a different receptor type, AMPA receptors, which triggers a cascade of intracellular signaling that ultimately promotes synaptic plasticity, or the strengthening and reorganization of neural connections (National Institutes of Health).

The Neuroplasticity Cascade

The AMPA activation that follows NMDA blockade sets off a series of events inside the neuron. Among the most important is the production and release of BDNF (brain-derived neurotrophic factor), a protein that supports the growth, survival, and formation of new synaptic connections (National Institutes of Health). BDNF is often called the brain’s fertilizer, and the analogy holds: it is what allows neurons to grow new dendritic spines: the tiny projections through which neurons receive signals from neighboring cells.

In a brain affected by depression or PTSD, this infrastructure has often been degraded. Chronic stress hormones suppress BDNF, weaken synaptic connections, and reduce the density of dendritic spines in regions like the prefrontal cortex and hippocampus, areas central to mood regulation, decision-making, and emotional context. Ketamine’s BDNF-stimulating effect begins reversing this within hours of infusion, which is the most credible explanation for why antidepressant effects appear so quickly compared to medications that require weeks to achieve similar downstream results.

Research published in Nature also points to a secondary mechanism: ketamine appears to interact with the brain’s opioid system in ways that may contribute independently to its antidepressant action (Nature). This suggests ketamine is not a single-pathway drug, it works through at least two distinct systems simultaneously, which may explain both its breadth of effect across different conditions and the variation in how individual patients respond.

Why IV Delivery Matters

Ketamine can be administered in several ways, intravenously, intramuscularly, as an intranasal spray, or as oral lozenges. Each route produces a different pharmacokinetic profile: different rates of absorption, different peak concentrations, different durations of effect.

IV delivery, the method used at Soft Reboot Wellness, produces the most precise and controllable pharmacological profile. The dose enters the bloodstream directly, with no absorption variability from the gut or nasal mucosa. Peak plasma levels are reached quickly and predictably. The physician can adjust the infusion rate in real time based on the patient’s response. For patients whose treatment history involves partial or inconsistent responses to other medication forms, this precision matters.

Dr. Sara Herman, our Harvard-trained anesthesiologist with more than two decades of experience administering IV medications, personally provides and monitors all infusion sessions. The clinical environment at our Menlo Park clinic includes continuous vital sign monitoring and immediate access to intervention if needed. The dose used in mental health treatment is a fraction of what is administered for surgical anesthesia, sub-anesthetic dosing is well-tolerated and carries a well-established safety profile when administered by qualified clinicians in an appropriately equipped setting.

The Hours and Days After Infusion

The acute pharmacological effects of a ketamine infusion, the altered perception, the dissociative quality, resolve fully within one to two hours of infusion completion. What persists is the neuroplastic change the infusion has initiated. BDNF levels remain elevated. New synaptic connections are forming. The brain’s default circuitry, including the default mode network, which governs self-referential thinking and is often overactive in depression, is temporarily reorganized.

The 48 to 72 hours following infusion represent what many clinicians describe as an integration window: the period during which the brain is most receptive to the consolidation of new patterns. This is why the timing of integration work matters. At Soft Reboot Wellness, our KAP program is structured specifically around this window, the preparation session happens before infusion, and the integration coaching sessions are timed to the period when the brain is most able to use the new neural architecture the infusion has created.

Research confirms that a series of infusions produces cumulative neuroplastic benefit, repeated sessions extend and deepen the changes initiated by the first (National Institutes of Health). Our standard induction protocol involves four to six IV infusions over four to six weeks, with the specific protocol calibrated to your clinical response and informed by mood data tracked through the Osmind platform throughout your treatment.

What the Pharmacology Means for Candidacy

The same mechanism that makes ketamine effective for many patients also creates genuine contraindications for others. Because ketamine increases blood pressure transiently during infusion, patients with uncontrolled hypertension or certain cardiovascular conditions require additional clinical judgment before proceeding. Patients with a history of psychosis or certain personality disorders may not be appropriate candidates, as the dissociative properties of ketamine carry different risk profiles in those populations. Active substance use disorders also require careful evaluation.

This is why the consultation and review process at Soft Reboot Wellness is thorough, not perfunctory. We review your full medical and psychiatric history, your current medications, and your prior treatment responses before making any recommendation. Results vary by individual, and we encourage you to discuss all options with your existing healthcare provider before deciding whether IV ketamine therapy is appropriate for you.

IV ketamine for mental health is an off-label treatment, and insurance coverage is not standard. We recommend contacting our team at 650-419-3330 or hello@softrebootwellness.com before your consultation so that cost is a clear part of your decision-making rather than a surprise afterward.

Frequently Asked Questions

Why does IV ketamine work faster than oral or nasal forms? IV delivery bypasses the absorption variability that affects oral and intranasal routes. The medication enters the bloodstream directly, reaching predictable peak plasma concentrations quickly and allowing the administering physician to adjust the dose in real time. This precision produces a more reliable pharmacological effect, which is one reason IV remains the method with the strongest clinical evidence base for psychiatric indications.

What is the difference between the acute effects of ketamine and the lasting antidepressant effects? The acute effects, altered perception, dissociation, dreamlike quality, are a product of active NMDA receptor blockade during the infusion and resolve within one to two hours. The lasting antidepressant effects are a product of the downstream neuroplastic cascade: BDNF elevation, synaptic connection formation, and dendritic spine growth that continue developing in the hours and days after the infusion ends. The experience and the therapeutic mechanism are related but distinct.

Does ketamine lose effectiveness over time with repeated infusions? Some patients do find that the response to maintenance infusions shifts over time, either diminishing or requiring different spacing. This is not universal, and the clinical picture varies considerably between individuals. We monitor response throughout treatment using mood tracking data and adjust the protocol accordingly. Some patients require only occasional boosters; others benefit from a more regular maintenance schedule.

How does the opioid system interaction affect the risk of dependence? The opioid system interaction identified in recent research does not mean ketamine functions as an opioid or carries comparable dependence risk. The interaction appears to occur at different receptor subtypes and at a different scale than classical opioid medications. Ketamine does carry its own potential for misuse at high doses outside clinical settings, which is one reason administration in a supervised clinical environment with appropriate screening is medically required.

Key Takeaways

• IV ketamine blocks NMDA receptors, triggering a compensatory glutamate surge that activates AMPA receptors and initiates a neuroplasticity cascade, the core mechanism of its antidepressant effect.
• BDNF elevation following infusion supports new synaptic connection formation in brain regions degraded by chronic depression or trauma.
• Emerging research suggests ketamine also interacts with the opioid system as a secondary pathway, pointing to a multi-mechanism pharmacological profile.
• IV delivery produces the most precise and controllable pharmacokinetic profile; Dr. Herman personally monitors all infusion sessions at our Menlo Park clinic.
• The 48 to 72 hours following infusion are the prime integration window; our KAP program is timed around this period to maximize the value of the neuroplastic changes ketamine initiates.

Knowing what ketamine does in the body, not just that it works, but how and why, puts you in a better position to decide whether it belongs in your treatment plan. We are glad to walk through that conversation in depth. Call us at 650-419-3330 or email hello@softrebootwellness.com to start the conversation.

References

1. National Institutes of Health. The glutamate neurotransmitter system is the brain’s primary excitatory system and a key pathway through which ketamine produces its therapeutic effects. https://www.ncbi.nlm.nih.gov/books/NBK62187/
2. National Institutes of Health. Ketamine promotes neuroplasticity, the brain’s ability to form new neural connections, which may explain its rapid and sustained antidepressant effects. https://pmc.ncbi.nlm.nih.gov/articles/PMC8190578/
3. National Institutes of Health. Ketamine has been shown to increase brain-derived neurotrophic factor (BDNF), a protein essential for neuron growth and long-term mood regulation. https://pubmed.ncbi.nlm.nih.gov/39684808/
4. Nature. Research suggests ketamine may also produce antidepressant effects by interacting with the brain’s opioid system, pointing to multiple mechanisms of action. https://www.nature.com/articles/s41591-025-03800-w
5. National Institutes of Health. Multiple ketamine infusion sessions have been shown to produce cumulative antidepressant benefits and extend remission periods in patients with depression. https://pmc.ncbi.nlm.nih.gov/articles/PMC6236511/

Medical Disclaimer: The information in this blog is for educational purposes only and does not constitute medical advice. Ketamine therapy should only be pursued under the supervision of a licensed medical provider familiar with your full medical and psychiatric history. Individual results vary. Off-label treatments like IV ketamine for mental health conditions carry risks that should be discussed thoroughly with a qualified provider before beginning. If you are experiencing a mental health crisis or thoughts of self-harm, please call or text 988 to reach the Suicide and Crisis Lifeline or go to your nearest emergency room.