Lexapro causes diarrhea because it raises serotonin levels in your gut, not just your brain. About 95% of the body’s serotonin is produced in the digestive tract, and when Lexapro blocks the reabsorption of that serotonin, the excess speeds up digestion and draws extra fluid into your intestines. In clinical trials, 8% of people taking Lexapro reported diarrhea, compared to 5–6% on a placebo.
How Serotonin Affects Your Gut
Lexapro (escitalopram) belongs to a class of antidepressants called SSRIs, which work by preventing cells from reabsorbing serotonin after it’s released. This leaves more serotonin available in the spaces between cells. The intended target is the brain, where higher serotonin levels can improve mood and reduce anxiety. But the same mechanism plays out in your digestive system, where serotonin has an entirely different job.
In the gut, serotonin regulates two things that matter here: how fast food moves through the intestines (peristalsis) and how much fluid gets secreted into the intestinal lining. When Lexapro increases the amount of serotonin floating around in your gut, it activates specific receptors on the cells that control the rhythm of intestinal contractions. These pacemaker cells respond to the extra serotonin by firing more frequently, which pushes food through faster than normal. At the same time, serotonin stimulates the release of acetylcholine, a chemical messenger that further accelerates movement through the colon and triggers fluid secretion into the intestinal space. The result is looser, more frequent stools.
This is why diarrhea is common across all SSRIs, not just Lexapro. Any drug that raises gut serotonin levels will have this effect to some degree.
How Common It Is, and Whether Dose Matters
FDA clinical trial data shows diarrhea affected about 8% of people taking Lexapro for depression or anxiety, versus 5–6% of those on a placebo. That gap is real but modest, meaning most people on Lexapro won’t experience significant diarrhea.
Dose makes a noticeable difference, though. In trials comparing the standard 10 mg dose to the higher 20 mg dose, diarrhea rates jumped considerably. At 10 mg per day, 6% of participants reported diarrhea (barely above the 5% placebo rate). At 20 mg per day, that number climbed to 14%, nearly triple the placebo rate. If you’ve recently had your dose increased and diarrhea started or worsened, the higher serotonin load in your gut is the likely explanation.
When It Typically Goes Away
For most people, diarrhea from Lexapro is a startup side effect that fades as the body adjusts. The general timeline for serotonin-related gut symptoms to improve is one to two weeks. What happens during that window is a process called receptor desensitization: the serotonin receptors in your gut, after being chronically overstimulated, gradually dial down their sensitivity. They don’t stop working entirely, but they stop overreacting to the increased serotonin supply.
If your diarrhea persists beyond three to four weeks without improvement, that’s a signal it may not resolve on its own. At that point, a conversation with your prescriber about adjusting the dose or trying a different medication is reasonable. Some SSRIs are more likely to cause GI problems than others, so switching can sometimes make a real difference.
What Helps in the Meantime
While you’re waiting for your gut to adapt, a few practical steps can reduce discomfort. Staying hydrated is the most important, since diarrhea pulls extra fluid into your intestines. Eating smaller, more frequent meals gives your digestive system less to process at once. Temporarily cutting back on high-fiber foods, caffeine, and dairy can also help, since all three independently speed up gut motility.
Taking Lexapro with food may blunt the initial serotonin surge in the gut, though this varies from person to person. Some people find that taking it at night, rather than in the morning, keeps the worst of the GI effects confined to sleep hours.
When Diarrhea Could Signal Something Serious
Ordinary Lexapro-related diarrhea is uncomfortable but not dangerous. There is one situation, however, where diarrhea alongside other symptoms requires urgent attention: serotonin syndrome. This is a rare but potentially life-threatening reaction that happens when serotonin levels climb too high, usually because of a drug interaction or a rapid dose increase.
Serotonin syndrome symptoms typically appear within hours of starting a new drug or increasing a dose. Diarrhea alone is not a red flag. But diarrhea combined with several of the following symptoms is: rapid heart rate, high blood pressure, agitation or restlessness, confusion, muscle twitching or rigidity, heavy sweating, dilated pupils, or shivering. Severe cases can involve high fever, seizures, or irregular heartbeat. If you notice a cluster of these symptoms developing quickly after a dose change, that warrants emergency care.
The risk of serotonin syndrome increases substantially when Lexapro is combined with other medications that raise serotonin, including certain migraine drugs, pain medications, herbal supplements like St. John’s wort, and other antidepressants. If you’re taking Lexapro alongside any of these and develop sudden, multi-symptom illness, take it seriously.