Can Ketamine Therapy Improve Concentration? Mechanism and Outcomes Explained

Depression and Concentration: Why Brain Fog Is a Common Symptom

Depression brain fog can show up as reading the same paragraph three times without taking it in, losing the thread of a conversation or a show, or struggling over small decisions. Clinically, it is trouble concentrating, remembering or making decisions, a recognized symptom of depression (National Institute of Mental Health).¹⁰ It is also one of the nine questions on the PHQ-9, the standard depression questionnaire.

Brain fog is common because depression affects the brain systems behind attention and memory:

• The planning center. The prefrontal cortex, which directs attention and planning, is one of the brain regions most consistently affected in depression (Pizzagalli and Roberts, 2022).¹¹
• The stress response. Depression often keeps the body's stress system switched on, and in one study, people with higher levels of cortisol, the main stress hormone, did worse on cognitive tests (Keller et al., 2017).¹²
• The memory center. Brain scans of more than 1,700 people with depression found a slightly smaller hippocampus, a region central to memory, mainly in people who had had repeated episodes (Schmaal et al., 2016).¹³

It is also one of the most widespread symptoms. In Mindbloom's analysis of 36,847 adults starting at-home ketamine therapy for depression, 53% had trouble concentrating on more than half the days (Carter et al., 2026).¹ In a three-year study of 267 people with depression, cognitive problems, low energy and sleep problems were present 85% to 94% of the time during depressive episodes (Conradi et al., 2011).¹⁴ It is not a character flaw. It is a known symptom of depression, and it is treatable.

Why Depression Brain Fog Often Outlasts Standard Antidepressants

Most antidepressants, including SSRIs, work mainly on serotonin to lift mood, so any help with focus tends to be indirect. In one meta-analysis of placebo-controlled trials, antidepressants had no significant effect on executive function, the skills that let you plan and stay on task (Rosenblat et al., 2016).¹⁵ As a result, concentration problems often remain after mood improves:

• In the large STAR*D study, about 1 in 5 people whose depression went into remission on citalopram (Celexa) still reported at least mild trouble concentrating or making decisions (Nierenberg et al., 2010).¹⁶
• A meta-analysis of cognitive testing found attention and planning difficulties in people whose depression had gone into remission (Rock et al., 2014).¹⁷

That gap is why researchers have looked at treatments that work on the brain differently, including ketamine.

Can Ketamine Therapy Help With Concentration? What the Research Shows

Yes. For the trouble concentrating and brain fog that come with depression, Mindbloom's new research shows that ketamine therapy can substantially reduce them: patients who started at-home treatment having trouble concentrating most days saw its severity drop 56% on average by Session 6, about six weeks in (Carter et al., 2026).¹

Real-World Results From 19,350 Patients

Mindbloom's analysis measured concentration with the PHQ-9 question that asks how often, over the past two weeks, a person has had "trouble concentrating on things, such as reading the newspaper or watching television." It followed the 19,350 patients who answered "more than half the days" or "nearly every day" at the start.¹ The table below shows how their answers changed at Sessions 2, 4 and 6.

Real-world preprint data (Carter et al., 2026). 19,350 patients at the start; 1,335 completed the Session 6 check-in.

Among the 1,335 who completed the Session 6 check-in:

• Severity of concentration problems dropped 56% on average.¹
• 74% went from having trouble concentrating most days to only occasionally or not at all (Mindbloom analysis of Carter et al., 2026).³
• 84% improved, meaning their answer dropped by at least one step on the 0 to 3 scale.¹
• More than 1 in 4 (28%) reported complete resolution of their concentration problems.¹
• Change showed up early: severity was already down 42% by Session 2, about two weeks in, and 71% had improved.¹
• In the full analysis of all nine PHQ-9 symptoms, concentration improved nearly as much as low mood, the core symptom of depression: 56% compared with 58%.¹

These results come from a retrospective analysis of real-world, patient-reported outcomes, posted as a preprint in October 2026.¹ Patients took ketamine as sublingual tablets or by subcutaneous injection, and results were combined across both; Mindbloom's peer-reviewed study of at-home subcutaneous ketamine reports that route on its own. Because PHQ-9 Item 7 is a single question rather than a cognitive test, some of the change may reflect mood improving overall.

What Clinical Trials Show About Ketamine and Cognition

Clinical trials test cognition directly, with timed tests of attention, memory and processing speed rather than a questionnaire. Their evidence is smaller and more mixed than Mindbloom's, and it is strongest for a course of treatment rather than a single dose. The table below summarizes four of the key studies.

All of these studies used IV ketamine in clinics. None tested sublingual tablets, injections under the skin or at-home treatment.

What those studies found:

• A course of infusions. In a randomized trial of people with treatment-resistant depression, those who had six IV ketamine infusions improved more on processing speed, mental flexibility and spatial working memory than those who had one, and the gains held after accounting for changes in depression (Shiroma et al., 2020).⁷
• A course of infusions, tied to mood. In an open-label study of 84 people with depression, processing speed and verbal learning improved after six IV infusions, but most of that change was explained by depression lifting (Zhou et al., 2018).¹⁸
• The review evidence. A 2026 review of 21 studies in treatment-resistant depression concluded that low-dose IV ketamine appeared to preserve or improve specific cognitive skills, especially processing speed, working memory and executive control, with no cognitive decline reported (Chavigny et al., 2026).²
• A single dose. In a randomized trial of 62 people with treatment-resistant depression, test scores a week after one IV infusion were no worse than before, but no better than in the comparison group either (Murrough et al., 2015).¹⁹

Put plainly, Mindbloom's real-world data and the clinical trials point the same way: ketamine therapy is associated with better concentration and cognitive function in people with depression. Whether that comes from ketamine acting on cognition directly or from depression easing is still an open question, and researchers say larger trials with cognition as the main outcome are needed (Vaccarino et al., 2022).⁹

Ketamine Therapy vs. Other Concentration Treatments: Antidepressants, Esketamine, TMS and Therapy

Below is a synthesis of how Mindbloom's at-home ketamine therapy results on concentration compare with studies of other treatments, first on the same PHQ-9 question and then on other measures of concentration.

Same PHQ-9 Question

The table below breaks down how Mindbloom's at-home ketamine therapy outcomes compare with studies of other treatments that used the same PHQ-9 concentration question.

Put plainly, here is how it compares:

• Comparable to esketamine (Spravato): 84% of Mindbloom patients improved by Session 6, vs. 81% with esketamine plus a new antidepressant at the end of a four-week induction (Carter et al., 2026; Floden et al., 2022).⁴
• Higher than an antidepressant alone: 84% vs. 74%, 10 percentage points higher than a new antidepressant started without esketamine (Floden et al., 2022).⁴
• Comparable to TMS, with a sixth as many sessions: a 56% average drop by Session 6 vs. 52% after a full course of at least 36 TMS sessions (Hutton et al., 2024).⁵
• Higher than talk therapy: a 56% average drop vs. 44%, 12 percentage points higher than seen from the first to the last session of CBT or counselling for depression in England's NHS Talking Therapies services (O'Driscoll et al., 2023).⁶

Other Concentration Measures

Other studies measured concentration with different questionnaires, so these comparisons are directional: Mindbloom asked a single PHQ-9 question, while these studies used other depression questionnaires or cognitive-complaint scales. The table below shows how the results line up.

Here is how those results compare:

• Higher than sertraline (Zoloft): a 56% average drop by Session 6 vs. 40% after 12 weeks in a large primary care trial, in about half the time (Piazza et al., 2025).²¹
• Higher than vortioxetine (Trintellix), an antidepressant studied for its effects on cognition: 56% vs. 41% reported after 24 weeks in routine care (Mattingly et al., 2022).²⁰
• Higher than computerized cognitive training: 56% vs. 35% after 12 weeks (Barlati et al., 2025).²²
• Higher than a course of IV ketamine: 56% vs. roughly 30% after seven infusions in one clinical study of treatment-resistant depression (Phillips et al., 2022).²³

Ketamine for ADHD: How ADHD Differs From Depression Brain Fog

Ketamine therapy is not prescribed for ADHD. Clinicians use it off-label for depression, and also for anxiety and PTSD. ADHD and depression often occur together, though, and the concentration problems can feel alike. The difference is in the pattern. ADHD is a long-term pattern of inattention or hyperactivity that begins in childhood (National Institute of Mental Health).²⁴ Depression brain fog, by contrast, tends to rise and fall with depressive episodes (Conradi et al., 2011).¹⁴ If you are not sure which is behind your trouble concentrating, a clinician can help sort it out, along with other possible causes such as sleep problems, thyroid conditions or low vitamin B12, and tell you whether ketamine therapy may be an option.

Ketamine's Effect on the Brain: How It May Support Concentration

What ketamine does in the brain differs from most antidepressants, which work mainly on serotonin. Ketamine works on glutamate, the brain's main excitatory messenger, setting off growth signaling and neuroplasticity, the formation of new connections between brain cells, though the exact steps are still debated (Krystal et al., 2024).²⁵ For concentration, research on how ketamine helps depression centers on the prefrontal cortex, the brain's planning center and one of the regions depression affects most.

• In people with depression. In a small brain-imaging study, the prefrontal cortex started out less connected to the rest of the brain than in healthy volunteers, and 24 hours after a single IV ketamine infusion, its connectivity had increased (Abdallah et al., 2017).²⁶
• In animals, new connections. In rats, a single low dose of ketamine quickly switched on a growth pathway called mTOR and increased the number of new connections between neurons in the prefrontal cortex within 24 hours (Li et al., 2010).²⁷
• In animals, restoring what stress removed. In mice given a chronic stress hormone, ketamine restored many of the prefrontal connections that stress had removed, and those new connections helped sustain its antidepressant-like effect over the following days (Moda-Sava et al., 2019).²⁸

The growth of new connections has been shown directly only in animals; in people, the evidence comes from brain scans and cognitive tests.

Is Ketamine Therapy Safe for Your Memory and Focus? What Research Shows

At the doses used for depression, ketamine's effects on attention and memory on session day appear to be temporary, and research to date, mostly short term, has not found lasting harm to cognition. A review of 17 studies found no negative effects on cognition from single or repeated IV ketamine in the two weeks after treatment (Vaccarino et al., 2022).⁹

Short-Term Effects of Ketamine: What to Expect on Session Day

• During the session. Ketamine produces dissociation, a dreamlike, detached state that many people find meaningful, and it usually fades as the session ends.
• In the hours after. In a study of 29 people with depression or PTSD and 29 healthy volunteers, a single IV dose lowered scores on tests of attention, executive function and verbal memory two hours later, and all had returned to baseline by the next day (Davis et al., 2021).⁸
• Why healthy-volunteer studies look different. Studies that show ketamine affecting memory in healthy volunteers usually test people during or right after dosing. In people with depression tested in the days after treatment, a review found no significant cognitive impairment (Shiroma et al., 2022).²⁹
• Driving. The FDA label for esketamine, a closely related drug, notes that it can affect attention, judgment, thinking, reaction speed and motor skills, and advises against driving until the next day after restful sleep (Janssen Pharmaceuticals).³⁰ For ketamine therapy, the guidance is the same: plan the post-session period for rest, and wait until after a full night of sleep to drive or do anything that needs full alertness.

Long-Term Effects on the Brain: What Repeated-Treatment Studies Show

• Compared with ECT. In a secondary analysis of a large randomized trial of 365 people with treatment-resistant depression, those who had six IV ketamine infusions scored better on all four cognitive tests at the end of a three-week course than those who had ECT, a treatment known for memory side effects, and the researchers concluded that both treatments appeared cognitively safe over longer follow-up (Kumpf et al., 2025).³¹
• Up to about a year. In an open-label study of esketamine, a related drug given as a nasal spray, cognitive performance generally improved or stayed stable over up to about a year of treatment (Wajs et al., 2020).³²
• What is not yet known. Few studies have followed cognition over months of repeated IV ketamine treatment, and researchers say the data are not yet enough to judge lasting effects (Vaccarino et al., 2022).⁹

Ketamine Brain Damage and Memory Loss: How Medical Use Differs From Recreational Use

Most research linking ketamine to memory loss and other cognitive harm comes from people who use it recreationally, often frequently and in large amounts. In a one-year study of people who use ketamine recreationally, cognitive deficits were seen mainly in frequent, heavy users (Morgan et al., 2010).³³ Medical treatment looks very different: prescribed doses, sessions spaced days apart, medical screening beforehand and medical oversight throughout. Those safeguards are designed to avoid the patterns linked to harm in recreational users, though the two have not been compared directly in a trial.

Other Side Effects and How They Are Monitored

Ketamine side effects are generally uncommon in people who pass medical screening, though ketamine therapy is not right for everyone. In Mindbloom's peer-reviewed study of 11,441 patients taking sublingual ketamine at home, no single side effect was reported by more than about 1% of patients at a check-in, and 0.4% of all patients stopped because of side effects (Mathai et al., 2024).³⁴

• Blood pressure: ketamine raises blood pressure temporarily, so it is checked around sessions.
• Misuse: ketamine can be misused, so at-home treatment involves medical screening and ongoing clinician oversight to manage addiction risk.