All Things Ketamine — The Most Comprehensive Podcast Episode Ever with Dr. John Krystal

Everyday sadness is a transient negative feeling, while clinical depression is a pervasive mode of being that invades all aspects of life, affecting thinking patterns, judgment, and emotional experience. It can manifest as a complete blunting of feelings, a dulling of perception, loss of energy, concentration issues, and pervasive negative thoughts. Furthermore, depression is a medical condition affecting the entire body, increasing inflammation and worsening other medical illnesses, potentially shortening life by an average of five years if untreated.

Psychiatry has historically struggled with partial responses, sometimes blaming the patient. However, partial recovery from depression, even if substantial, leaves patients symptomatic in ways that harm social relationships and productivity. Many healthcare systems lack routine outcome measures, making inadequate responses invisible. It is crucial to keep pressing for full remission because unexplored treatment options often exist, and ongoing symptoms severely impact a patient's overall health and lifespan.

The serotonin hypothesis, prevalent since the 1950s, suggested depression was due to a serotonin deficit. However, studies showed that depleting serotonin in healthy people didn't cause depression, demonstrating this simple model was insufficient. This led researchers, including Dr. Krystal and Dennis Charney, to 'turn the brain on its head' and consider higher cognitive and emotional centers driven by glutamate, which accounts for 90% of brain synapses, compared to serotonin's 2%.

Dr. Krystal's team initially used ketamine to study cognitive impairments in schizophrenia due to its ability to probe glutamate synaptic signaling. Accidentally, in a study with depressed patients, they observed rapid and profound antidepressant effects within 24 hours of a single dose. This finding, first presented in 1997 and replicated in 2006, was initially met with skepticism but eventually led to widespread clinical adoption.

Research by Ron Duman and George Aghajanian in 2010 showed that a single dose of ketamine could rapidly restore synaptic connections lost due to chronic stress in animal models. Ketamine indirectly increases glutamate release, which triggers the elevation of Brain-Derived Neurotrophic Factor (BDNF) and activates the Mtor pathway, leading to the regrowth and stabilization of synaptic connections. This process helps restore the brain's intrinsic capacity for resilience.

The role of dissociation is complex. While some guided experiences during dissociation can be meaningful, many patients achieve antidepressant effects without finding the dissociative experience productive or memorable. However, for patients with pre-existing synaptic deficits, dissociative symptoms during ketamine infusion can be a marker that enough ketamine has reached the brain to trigger therapeutic effects and increase synaptic density. For others without these deficits, dissociation may be unrelated or even slightly counterproductive to clinical improvement.

Current best practices for treatment-resistant depression typically involve a 40-minute intravenous infusion of 0.5 milligrams per kilogram of racemic ketamine. If well-tolerated, some clinicians may increase to 0.6 or 0.7 mg/kg. Dosing is highly specific; doses much lower than 0.5 mg/kg are largely ineffective. Treatment usually starts with twice-weekly infusions for four weeks, gradually reducing to once a week, then every other week, and eventually once a month for maintenance.

While medical use of ketamine is generally safe, abuse carries significant risks. Regular, high-dose ketamine use, common in some parts of the world, can lead to tolerance, physical and psychological dependence, and paradoxical increases in depressive symptoms. Chronic abuse can cause reductions in white matter, impaired brain function, lasting cognitive impairments, and persistent psychosis that is difficult to treat. The risk is particularly high for individuals with pre-existing substance use disorders.

Yes, ketamine is effectively used in pain centers to treat pathological pain. It blocks NMDA receptors in pain pathways in the spinal cord and higher executive pain centers, reducing both the experience and emotional impact of pain. Moreover, ketamine can prevent the development of tolerance to opioids and prevent the sensitization of pain pathways, making it useful in surgical procedures to reduce the risk of chronic neuropathic pain post-operatively. The pain relief can be remarkably durable, lasting for months, possibly by disrupting maladaptive pain-related learning and increasing resilience to pain.

Research focuses on making ketamine's rapid effects more lasting. One promising area involves co-administering ketamine with drugs like Rapamycin, an mTOR blocker. A preliminary study showed that a single dose of Rapamycin significantly extended ketamine's antidepressant response. The hypothesis is that Rapamycin's immunosuppressive effects might prevent microglia (immune cells in the brain) from 'gobbling up' newly formed synapses, thus stabilizing the neuroplastic changes induced by ketamine. Other strategies include developing new nmda receptor antagonists or combining ketamine with anti-addiction medications.

Exercise is known to have dose-related antidepressant effects, partly by increasing brain-derived neurotrophic factor (BDNF) in the brain. BDNF is crucial for both synaptic efficacy (making neurons more receptive to glutamate) and synaptic number, promoting the regrowth and stabilization of connections. Studies suggest that exercise, particularly team exercise, can significantly improve mood. The increase in BDNF from exercise may synergize with antidepressant treatments like SSRIs and ketamine, which also raise BDNF levels.

Within 5-10 years, new nmda receptor antagonists, including specific subtypes like nr2b antagonists and R-ketamine, along with combination therapies aiming to reduce abuse potential, are expected to be refined. In the psychedelic space, a key concept is developing 'non-hallucinogenic psychedelics' that trigger therapeutic neuroplasticity (e.g., via serotonin 2A receptors signaling through canonical pathways) without causing the subjective psychedelic experience. This approach aims to make treatments more accessible and easier to prescribe, though some argue the psychedelic experience is integral to the therapeutic outcome.