The most common side effect of sertraline is nausea, affecting roughly 25% of people who take it. Other frequent side effects include diarrhea, insomnia, dry mouth, fatigue, and dizziness. Most of these appear within the first week and improve significantly after about four weeks as your body adjusts to the medication.
Digestive Side Effects
Nausea tops the list because sertraline doesn’t just work in the brain. The same serotonin transporter it blocks in your central nervous system also exists throughout your gut. When sertraline raises serotonin levels in the digestive tract, that extra serotonin stimulates nerve endings that send signals to the brain’s nausea center. The result is a queasy feeling that’s most noticeable when you first start the medication or after a dose increase.
Diarrhea and loose stools follow a similar logic. Higher serotonin levels in the intestines speed up the muscular contractions that move food through your system and increase fluid secretion into the intestinal lining. This combination means faster transit and looser stools, particularly in the first few weeks. Eating a small meal before taking your dose and staying hydrated can help take the edge off both nausea and diarrhea while your body adjusts.
Sleep Changes and Fatigue
Insomnia affects about 16% to 17% of people taking sertraline. It can show up as difficulty falling asleep, waking in the middle of the night, or feeling like your sleep was lighter than usual. Some people experience the opposite: excessive drowsiness or daytime sleepiness. In one naturalistic study of patients on SSRIs, 59% reported somnolence as a noticeable symptom. Taking sertraline in the morning rather than at night can help if insomnia is the problem, while people who feel drowsy during the day sometimes do better taking it in the evening.
Fatigue (reported by 45% in the same study) often overlaps with sleepiness but feels distinct. It’s more of a low-energy, sluggish quality that doesn’t necessarily improve with more sleep. For most people, this fades within the first month.
Dry Mouth, Sweating, and Other Physical Effects
Dry mouth is surprisingly common, showing up in as many as 45% of SSRI users in real-world surveys. Sipping water throughout the day, chewing sugar-free gum, or using a saliva substitute can help. Increased sweating affects roughly 38% of users. Lightheadedness (43%) and yawning (47%) round out the physical side effects that people notice most often but rarely hear about before starting the medication.
Sexual Side Effects
Sertraline frequently affects sexual function. Reduced libido, difficulty reaching orgasm, and delayed ejaculation are all well-documented effects of SSRIs as a class. These side effects are underreported in clinical trials because patients often don’t volunteer the information unless asked directly. Unlike nausea or insomnia, sexual side effects don’t always improve with time and can persist for as long as you take the medication. If this becomes an issue, there are strategies your prescriber can discuss, including dose adjustments or switching to a different antidepressant with a lower risk profile for sexual function.
Emotional Blunting
About 46% of people taking SSRIs report a phenomenon called emotional blunting: a feeling that both positive and negative emotions are muted. You might notice you can’t cry at things that would normally make you tear up, or that moments of joy feel flattened. Some people describe it as watching life through glass. Around 20% of SSRI users specifically report an inability to cry, and about 30% experience a form of emotional apathy.
This side effect is slightly more common in men (52%) than women (44%) and tends to be more pronounced in people whose depression or anxiety symptoms are more severe. It can be difficult to tease apart from the emotional numbness that depression itself causes, which is one reason it often goes unrecognized. If you feel like the medication has traded sadness for feeling nothing at all, that’s worth raising with your prescriber, as it’s a recognized side effect, not just a personality change.
Weight Changes Over Time
In the short term, sertraline is relatively weight-neutral. At six months, the average weight gain is less than half a pound. But the picture shifts over longer use. By 24 months, the average gain is about 3.2 pounds, according to data reviewed by Harvard Health. That’s modest compared to some other antidepressants, but it adds up for people who are already managing their weight carefully. Changes in appetite (both increased and decreased) can appear early in treatment, and weight gain that does occur tends to creep in gradually rather than arriving all at once.
When Side Effects Typically Fade
Most of the early side effects, especially nausea, diarrhea, sleep disruption, and dizziness, begin within the first week of starting sertraline and resolve within about four weeks. Starting at a lower dose and increasing gradually every four weeks is the standard approach to minimize this adjustment period. Side effects are most noticeable during those initial weeks of dose changes.
Some side effects, however, don’t follow this timeline. Sexual dysfunction and emotional blunting tend to persist for as long as you’re on the medication. Weight gain is a slow, cumulative effect. Knowing which side effects are temporary and which may stick around can help you set realistic expectations.
Cognitive Effects
Memory impairment and decreased concentration are reported by roughly half of SSRI users in real-world surveys (51% and 50%, respectively). These can be difficult to separate from the cognitive fog that depression and anxiety already cause, but some people notice a distinct change after starting sertraline. For most, this improves as the medication reaches a steady state in the body, though a minority of people find it persistent enough to discuss alternatives with their prescriber.
Serious but Rare Risks
Serotonin syndrome is the most dangerous potential complication. It occurs when serotonin levels climb too high, usually because sertraline is combined with another medication that also raises serotonin (certain migraine drugs, other antidepressants, or specific pain medications). Symptoms include agitation, confusion, rapid heart rate, high blood pressure, muscle twitching or rigidity, and in severe cases, dangerously high body temperature. This is a medical emergency, but it’s rare when sertraline is taken on its own at prescribed doses.
For adults over 65, sertraline carries a specific risk of lowering sodium levels in the blood, a condition called hyponatremia. The risk is highest within the first two weeks of treatment. Symptoms include headache, confusion, nausea, and in severe cases, seizures. People who have experienced low sodium in the past for any reason are more likely to experience it again on sertraline.
Sertraline also carries an FDA boxed warning about increased risk of suicidal thoughts and behavior in children, adolescents, and young adults during the early phase of treatment. This doesn’t mean the medication causes suicidal feelings in most people. It means that close monitoring is especially important in younger patients during the first weeks, when the medication’s activating effects may arrive before its mood-stabilizing benefits fully kick in.