Lexapro causes tiredness because it increases serotonin levels in the brain, and serotonin plays a direct role in regulating sleep and wakefulness. In clinical trials, about 6% of people taking Lexapro reported sleepiness compared to 2% on a placebo, and 5% reported fatigue compared to 2% on placebo. So while it doesn’t make everyone tired, the effect is real and measurably more common than what you’d expect from taking a sugar pill.
How Serotonin Affects Your Energy
Lexapro (escitalopram) is a selective serotonin reuptake inhibitor, or SSRI. It works by blocking the reabsorption of serotonin in the brain, leaving more of it available in the spaces between nerve cells. This is what helps with depression and anxiety. But serotonin doesn’t just regulate mood. It’s also deeply involved in your sleep-wake cycle, and flooding the system with more of it can tip the balance toward drowsiness in some people.
Specifically, serotonin is a precursor to melatonin, the hormone that tells your body it’s time to sleep. More serotonin activity can mean more raw material for melatonin production. Serotonin also activates certain receptors in the brain that promote sedation. The net result for some people is a noticeable drag on daytime energy, especially in the first few weeks.
Lexapro Changes How You Sleep
Beyond general drowsiness, Lexapro alters the structure of your sleep itself. SSRIs are well-known suppressors of REM sleep, the phase of sleep associated with dreaming and memory consolidation. Research from the Cleveland Clinic has shown that people taking REM-suppressing antidepressants have dramatically reduced REM activity. In one study, the odds of entering REM sleep normally were at least 89% lower in people still taking these medications compared to those who had stopped for two weeks or more.
What does that mean for you? REM sleep is part of what makes sleep feel restorative. When it’s suppressed, you can clock a full eight hours and still wake up feeling groggy or unrefreshed. This is different from simply being sleepy during the day. It’s a qualitative change in how well your sleep actually works.
Higher Doses Cause More Fatigue
The tiredness effect is clearly dose-dependent. FDA fixed-dose trial data makes this stark:
- Placebo: 1% reported sleepiness
- 10 mg/day Lexapro: 4% reported sleepiness
- 20 mg/day Lexapro: 9% reported sleepiness
The overall rate of side effects in the 10 mg group (66%) was close to the placebo group (61%), but it jumped to 86% in the 20 mg group. So if you’ve recently gone from 10 mg to 20 mg and suddenly feel more wiped out, that tracks with what clinical data would predict. The fatigue pattern followed the same curve: 2% at placebo, 2% at 10 mg, and 6% at 20 mg.
When the Tiredness Typically Fades
For most people, the fatigue is worst during the first two weeks and gradually fades as your body adjusts to the medication. Side effects during this initial window tend to be mild and transient, decreasing in both intensity and frequency with continued treatment. Many people find the tiredness lifts within about a month, though for some it takes closer to two months before energy levels feel normal again.
If you’re in week one or two and struggling to keep your eyes open at 2 p.m., that’s a common experience and not necessarily a sign that the medication is wrong for you. The adjustment period is real, and pushing through it often pays off.
Tiredness vs. Emotional Blunting
Not everything that feels like tiredness on Lexapro is actually sleepiness. Some people experience something called emotional blunting, a flattening of both positive and negative emotions that can easily be mistaken for fatigue. You’re not drowsy exactly, but you feel flat, unmotivated, and low-energy. Things that used to excite you don’t anymore, and it’s tempting to describe that as “tired.”
Emotional blunting is distinct from both sleepiness and the loss of pleasure (anhedonia) that comes with depression itself. It’s a unique side effect of antidepressant treatment where the range of emotions narrows. Love, affection, fear, and anger all feel muted. If your “tiredness” feels more like you just don’t care about anything rather than a physical need to close your eyes, emotional blunting may be a better explanation, and it’s worth raising with your prescriber because the solutions are different.
What You Can Do About It
The simplest adjustment is changing when you take your dose. If Lexapro makes you drowsy during the day, taking it at night lets the peak sedation hit while you’re sleeping anyway. This is a widely recommended first step and doesn’t require any change to your prescription.
If the fatigue persists beyond the adjustment period and switching to a nighttime dose doesn’t help, there are a few paths forward. Your prescriber may consider lowering your dose, since the jump from 10 mg to 20 mg roughly doubles the sleepiness rate. For people who are responding well to Lexapro’s antidepressant effects but struggling with persistent low energy, adding a second medication that works on different brain chemicals (specifically norepinephrine and dopamine rather than serotonin) is a common strategy. These activating medications are sometimes chosen precisely because they target fatigue, poor concentration, and low motivation without adding to the serotonin load that’s causing the problem.
Basic sleep hygiene also matters more on Lexapro than off it. Because the medication is already disrupting your sleep architecture by suppressing REM sleep, anything else that degrades sleep quality (alcohol, irregular bedtimes, screens before bed) compounds the problem. Keeping a consistent sleep schedule gives your brain the best chance to get restorative sleep even with altered REM patterns.