Ketamine can make you tired, and it’s one of the more common side effects. In clinical trials of esketamine (the nasal spray form), roughly half of participants experienced sedation during treatment sessions. Even with standard intravenous ketamine, about 9.5% of patients report fatigue as a distinct side effect, and the drowsiness that follows a session can linger for one to two days.
How Common Sedation and Fatigue Are
The best data on ketamine-related tiredness comes from FDA clinical trials for esketamine, the prescription nasal spray used for treatment-resistant depression. In three short-term trials, sedation rates ranged from about 49% to 61% among people receiving esketamine, compared to just 10% to 19% in the placebo groups. That makes sedation one of the most frequently reported side effects, not a rare occurrence.
Severe sedation, where a person becomes very difficult to rouse, was uncommon. Fewer than 3% of participants experienced it in any trial. Most people who felt sedated described something milder: a heavy, drowsy, slowed-down feeling during and shortly after the treatment session. In longer-term maintenance use, sedation rates dropped to about 27%, suggesting the body partially adjusts over repeated sessions.
With standard intravenous ketamine at sub-anesthetic doses (the kind used in ketamine clinics for depression or pain), the fatigue rate in pooled studies sits around 9.5%. The difference likely reflects how the drug is delivered and dosed rather than a fundamentally different effect. Both forms act on the same brain pathways.
Why Ketamine Causes Drowsiness
Ketamine’s primary job in the brain is blocking a specific type of receptor involved in excitatory signaling. This triggers a surge of glutamate, the brain’s main “activating” chemical messenger, particularly in the prefrontal cortex. That burst of glutamate kicks off a cascade that strengthens connections between brain cells and, in people with depression, can rapidly improve mood.
But that same process also reshapes how the brain handles sleep and wakefulness. Research shows that in people with depression, a positive response to ketamine is linked to decreased time spent awake and increased total sleep time, including more deep sleep (slow-wave sleep) and more REM sleep. Essentially, the brain’s recovery and repair processes ramp up. This isn’t a malfunction. It’s part of how ketamine appears to work, restoring healthier sleep patterns that depression often disrupts.
The tiredness you feel after a session may partly reflect this shift. Your brain is doing more restorative work than it was before, and that takes energy. For people who’ve been sleeping poorly due to depression, the initial experience can feel like sudden, heavy fatigue even though the underlying change is beneficial.
How Ketamine Changes Sleep Patterns
Ketamine doesn’t just make you sleepy in the moment. It alters your sleep architecture for at least a couple of nights afterward. On the first night after an infusion, studies show increased total sleep time, more deep sleep, and a greater percentage of time spent in REM sleep, with less time lying awake. By the second night, the deep sleep boost may fade, but improvements in total sleep, REM sleep, and sleep efficiency (less waking up in the middle of the night) can persist.
One study found that ketamine reduced REM sleep on the night of administration itself, with no significant effect on total sleep time or the lighter sleep stages. The discrepancy between studies likely comes down to timing and context: whether the ketamine was given earlier in the day or closer to bedtime, and whether the person had depression or was otherwise healthy. In depressed individuals specifically, the sleep improvements tend to track closely with mood improvement, meaning better sleep after ketamine is generally a good sign.
How Long the Tiredness Lasts
Most people feel noticeably tired for 24 to 48 hours after a ketamine infusion or nasal spray session. The acute sedation during and immediately after treatment typically resolves within a few hours, but a subtler fatigue often carries into the next day. For some people it feels like the heaviness after a long flight or a particularly deep nap. By the 48-hour mark, most patients report that the fatigue has lifted and, in many cases, been replaced by improved energy and mood.
This timeline varies. People receiving their first treatment tend to feel more fatigued than those who’ve had several sessions. Higher doses produce more sedation. Your baseline sleep quality, other medications, and individual brain chemistry all play a role. Some people bounce back within hours, while others feel wiped out for a full two days.
Because of this lingering drowsiness, medical guidelines are clear: you should not drive, operate heavy machinery, or do anything requiring sharp reflexes for at least 24 hours after receiving ketamine. If you’re getting treatment at a clinic, plan to have someone drive you home and keep your schedule light for the rest of the day.
Tiredness vs. Feeling Energized
Here’s the part that surprises many people: ketamine can also make you feel more energized in the days following treatment. The initial fatigue and the later energy boost aren’t contradictory. They appear to be two phases of the same process. The brain undergoes a period of intense synaptic remodeling after ketamine exposure, strengthening neural connections that depression or chronic pain had weakened. That remodeling is metabolically demanding, which may explain the short-term exhaustion. Once it’s complete, many people report feeling more alert, motivated, and rested than they have in months.
Not everyone experiences both phases equally. Some people feel minimal fatigue and notice the mood lift almost immediately. Others go through a pronounced “crash” before improvement sets in. If you’re receiving ketamine for depression and feel unusually tired after your first session, that pattern is well within the normal range and doesn’t mean the treatment isn’t working. In fact, the research suggests the opposite: sleep changes after ketamine tend to correlate with a stronger and more lasting antidepressant response.
Practical Tips for Managing Post-Treatment Fatigue
- Schedule sessions strategically. If possible, book your treatment on a day when you can rest afterward. Late-week sessions work well for people who can take it easy over the weekend.
- Arrange transportation in advance. You’ll need a ride home, and you shouldn’t plan on driving until the following day at the earliest.
- Stay hydrated and eat lightly. Dehydration and low blood sugar can amplify the drowsy feeling. A light meal a couple hours before treatment and steady water intake afterward help.
- Don’t fight the sleepiness. If your body wants to nap after treatment, let it. The restorative sleep that follows ketamine appears to be part of the therapeutic process.
- Track your pattern over multiple sessions. Many people find the fatigue becomes more predictable and milder with repeated treatments. Keeping a simple log of how you feel at 2, 12, 24, and 48 hours can help you and your provider adjust timing and dosing.