Remeron Side Effects: Sleepiness, Appetite and What Else to Expect
The most common Remeron (mirtazapine) side effects are sleepiness, a bigger appetite and weight gain.
By withClaro Editorial · 2026-11-02 · 4 min read
Clinical section reviewed by Dr. Jason Tan , Consultant Psychiatrist, on October 27, 2026.
Key takeaways In the FDA trials, sleepiness affected 54% of people on Remeron against 18% on placebo. A bigger appetite and weight gain were the next most common side effects. On Reddit, weight gain or a bigger appetite and tiredness were the side effects people named most, by 45 and 41 of 85. Thoughts of self-harm in the first months or after a dose change, especially at 24 or younger, need a call to your prescriber the same day. Call your prescriber about a sore throat, fever or mouth sores, which can be signs of a rare drop in white blood cells. On this page
What are the most common side effects of Remeron? What side effects did people on Reddit describe on Remeron? Which Remeron side effects are serious? Do Remeron sleepiness and appetite changes go away? What should you tell your prescriber about Remeron side effects? Sleepiness leads the Remeron side effects: in the FDA trials for depression, it affected more than half of people on Remeron (mirtazapine), 54% against 18% on placebo, and about 1 in 10 stopped because of it. Appetite and weight gain come next. The label recommends taking it in the evening, before sleep.
What are the most common side effects of Remeron?
Sleepiness first, then a bigger appetite and weight gain. The label recommends taking Remeron in the evening, before sleep, so the sleepiness falls at night. The figures come from 6-week depression trials with 453 people on Remeron and 361 on placebo; the side effects seen at least twice as often as on placebo were:
Side effect Remeron Placebo Sleepiness 54% 18% Increased appetite 17% 2% Weight gain 12% 2% Dizziness 7% 3%
Two others were common but less than twice as often as on placebo: dry mouth, 25% against 15%, and constipation, 13% against 7%. Abnormal dreams affected 4%, against 1%. The 12% weight gain counts people whose gain was recorded as a side effect; 7.5% gained at least 7% of their body weight, against none on placebo, and in longer open studies 8% stopped Remeron because of weight gain.
What side effects did people on Reddit describe on Remeron?
These are people's own accounts, not trial measurements, and people with ongoing problems are more likely to post, so treat them as a range of experiences rather than odds. We read 88 recent threads on r/Anxiety, r/antidepressants and other subs where people discussed mirtazapine, comments included. Of 93 people who described their own experience, 85 named at least one side effect, and one person could name several:
What they named Of 85 people Weight gain or bigger appetite 45 Tiredness or drowsiness 41 Vivid dreams 11 Dizziness 9 Trouble sleeping 7 Brain fog 7
One person on Reddit wrote:
I also get the fatigue and groggy feeling upon waking up
Only 2 of the 93 said Remeron gave them nothing to report; one wrote:
the Mirtazapine hasn’t given me any major side effects
Which Remeron side effects are serious? Medically reviewed by Dr. Jason Tan on October 27, 2026, this section only.
The label's boxed warning is about suicidal thoughts and behavior in young people. Across antidepressant trials, there were 14 more cases per 1,000 people under 18 than on placebo, and 5 more per 1,000 at 18 to 24; from 25 up there were fewer cases than on placebo. The risk is highest in the first months and after a dose change.
The label also warns about agranulocytosis, a rare and serious drop in white blood cells: 2 of 2,796 people in the trials. Sore throat, fever, mouth sores or other signs of infection need a call to your prescriber right away. The severe drops in the trials came in the first two months, on days 9, 14 and 61. A rash with fever or swollen glands can be a sign of DRESS, a rare severe drug reaction, and also needs a call right away. Other warnings cover serotonin syndrome, heart rhythm changes, low sodium and higher cholesterol. If you notice any of these signs, call rather than wait for your next visit. The clinical view:
Most early side effects of antidepressants ease within the first weeks, while a few tend to last and are worth raising.
Call your prescriber the same day, or get urgent care, if you notice:
- new or worse thoughts of suicide or self-harm, especially early on, after a dose change, or in people under 25 - agitation, heavy sweating, fever, muscle twitching or confusion, which can be signs of serotonin syndrome - unusual bleeding or bruising, black or tarry stools, or vomiting blood - a sudden burst of energy, little need for sleep, racing thoughts or unusual risk-taking, especially if you or a close relative has bipolar disorder If you're having thoughts of harming yourself, contact emergency services or a crisis line straight away. In the US, call or text 988. In the UK, call Samaritans on 116 123. Elsewhere, find a crisis line near you .
Do Remeron sleepiness and appetite changes go away?
Not always. The label says it is unclear whether people get used to the sleepiness, and appetite and weight gain often continue while you take it. On Reddit, only 12 of 85 people said how long their side effects lasted, too few to count shares: 4 said they eased within weeks and 8 that they were still going. If sleepiness or appetite is still a problem after the first weeks, tell your prescriber. Both have their own pages: Remeron and weight gain and whether Remeron makes you tired .
What should you tell your prescriber about Remeron side effects?
Tell your prescriber which side effects you have, when they started and whether they are easing. It helps to tell them:
When you started Remeron, your dose and any recent change. How sleepy you feel in the morning and during the day. Changes in appetite since starting. Any sore throat, fever or infection. Other medicines that make you sleepy, and how much alcohol you drink. Download on the App Store Sleepiness and appetite on Remeron can shift over weeks. The withClaro app lets you log sleep, appetite, energy and mood each day, linked to your dose, and turns it into a report for your prescriber.
Frequently asked questions Does Remeron make you sleepy the next day? It can: morning grogginess is one of the most common complaints on Reddit, and the label warns it can slow thinking and reactions. If you still feel heavy in the morning after the first weeks, tell your prescriber.
Can I drive on Remeron? The label asks you not to drive or use dangerous machinery until you are reasonably sure Remeron doesn't affect your ability to do so. If you feel drowsy, don't drive.
Does a higher dose of Remeron make you sleepier? It can for some: one person on Reddit found 30 mg more sedating than 15 mg. Tell your prescriber how sleepy you are after each dose change.
Can you drink alcohol on Remeron? The label advises avoiding alcohol on Remeron, because both slow thinking and movement and the effects add up. Talk to your prescriber if that is hard for you.
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Sources REMERON (mirtazapine) prescribing information, US Food and Drug Administration via DailyMed, revised November 2021 Claro articles are for self-monitoring and educational purposes only. They are not a medical device, therapist, or diagnostic tool, and do not replace care from your prescribing clinician. If you are in crisis, contact your care team, emergency services, the Samaritans (UK: 116 123), or the Crisis Text Line (US: text HOME to 741741).