The short answer: Most standard antidepressants take 4 to 8 weeks to work, according to the National Institute of Mental Health. Sleep, appetite, energy and concentration often improve before mood does. NICE says that if a drug is going to work, the effect usually shows within 4 weeks. Full remission often takes longer, and in the largest real-world trial many people got there only at or after week 8.
Which symptoms improve first, and which improve last?
Depression is a cluster of symptoms, and they do not all lift at once. NIMH states that problems with sleep, appetite, energy and concentration often improve before mood lifts. That order matters, because it changes what you should look for in the first month.
Many people expect to wake up one day feeling happy. What usually happens is quieter. You fall asleep a little easier. You finish a meal. You get through a work task without rereading the same paragraph five times. The low mood and the loss of interest tend to be the last things to shift.
This is also why people close to you may notice a change before you do. A partner may see that you are getting out of bed on time while you still feel flat inside. That is a real sign of progress, not an illusion.
One caution: early energy can arrive before mood improves. NIMH advises that people of all ages taking antidepressants be watched closely, especially during the first few weeks. Tell someone at once if thoughts of self-harm appear or get worse.
What do the first two weeks tell you?
More than people are usually told. A meta-analysis of 41 trials with 6,562 patients defined early improvement as at least a 20% drop on the Hamilton depression scale within 2 weeks. Early improvement predicted later stable response with a sensitivity of at least 81%, and stable remission with at least 87%.
The more useful number is the reverse. Negative predictive values ranged from 82% to 100%. In plain terms, people with no improvement at all by week 2 had little chance of a stable response on that drug. The authors concluded that a lack of early improvement may justify considering a change sooner than usual.
A later analysis adds an important check. An individual patient data meta-analysis of 30 trials, covering 6,058 people on antidepressants and 2,184 on placebo, found that week 2 improvement predicts outcome only moderately. Of people predicted not to respond, 29% did respond by week 6 and 43% by week 12. The authors warned that routinely changing treatment because of limited early improvement would often be premature.
So treat week 2 as a signal, not a verdict. Some improvement is a good sign. No change at all is worth raising with your prescriber, but it does not mean the drug has failed.
How long should you give one antidepressant before judging it?
Guidelines converge on about 4 weeks at a proper dose before judging whether a drug is doing anything. The NICE depression guideline (NG222) says people should be told that, if an antidepressant is going to work, it usually does so within 4 weeks.
NICE also sets out a review schedule:
- A first review, usually within 2 weeks, to check that symptoms are improving and to look at side effects.
- A review at 1 week for people aged 18 to 25, or when there is a particular concern about suicide risk.
- A treatment review between 2 and 4 weeks after starting any depression treatment.
If depression has not responded at all after 4 weeks at a recognised therapeutic dose, NICE recommends a structured discussion. That covers whether the drug is being taken as prescribed, whether side effects are a problem, and whether other life or health factors are getting in the way.
Partial improvement is different from none. If you are somewhat better at week 4, many prescribers will continue or adjust the dose and reassess over the following weeks. That fits the NIMH 4 to 8 week window. Side effects run on a separate and usually faster clock, which we cover in how long SSRI side effects last.
How long does it take to feel fully well again?
Longer than it takes to feel better. Response usually means a 50% drop in symptom scores. Remission means symptoms have mostly gone. They are not the same milestone.
The STAR*D trial is the best real-world guide. In its first step, 2,876 outpatients took citalopram for up to 14 weeks with regular symptom measurement. The response rate was 47%. Remission rates were 28% on the Hamilton scale and 33% on a self-report scale. A substantial portion of those who reached response or remission did so at or after 8 weeks.
That last finding is the practical one. Some people who are only partly better at week 6 go on to remit if treatment continues and the dose is optimised.
The summary STAR*D report gave remission rates of 36.8%, 30.6%, 13.7% and 13.0% across four sequential steps, with a cumulative rate of 67%. A 2023 reanalysis of the patient-level data using the protocol's original outcome measure put cumulative remission at 35.0%. Both analyses agree on the direction: each later step helps fewer people, and reaching remission can take several months across more than one treatment.
Once you are well, the timeline changes again. Staying on treatment after remission is a separate question, covered in how long to stay on antidepressants.
Are any antidepressants faster than the usual 4 to 8 weeks?
Yes, three FDA-approved products show effects within days in their label data. Each has a narrow use.
- Esketamine (Spravato). A nasal spray for treatment-resistant depression, and for depressive symptoms in adults with major depression and acute suicidal thoughts or behavior. In one 4-week trial, the label reports that most of the difference from placebo was seen at 24 hours. In a monotherapy trial, improvement was statistically superior to placebo at Day 2 (about 24 hours). It is given only in certified settings under a REMS program, with monitoring for at least 2 hours after each dose.
- Dextromethorphan-bupropion (Auvelity). An oral tablet approved for major depressive disorder in adults. The primary outcome was measured at week 6, but the label reports a statistically significant difference from placebo at Week 1 and Week 2.
- Zuranolone (Zurzuvae). An oral 14-day course. It is FDA-approved only for postpartum depression in adults, not general depression. The primary endpoint was improvement at Day 15, and both pivotal trials met it.
These are not simply faster versions of an SSRI. Each has its own safety warnings, and esketamine requires clinic visits. For how they fit into later-line care, see treatment-resistant depression.
What should you do if nothing has changed?
Do not stop on your own. Book a review instead. Stopping suddenly can cause withdrawal symptoms, and the options are wider than "keep waiting" or "quit."
After a trial that has not worked, NICE lists options such as increasing the dose, switching to another antidepressant, adding another medication, switching to psychological therapy, or adding a group exercise program. NICE also advises reviewing the diagnosis if several treatments have not helped. Anxiety, bipolar disorder and sleep disorders can all look like stubborn depression. If worry is the dominant problem, anxiety.md covers that side.
It helps to track two or three symptoms each week, such as sleep, energy and interest. That gives your prescriber something concrete to judge at the 2 and 4 week reviews.
The bottom line
Expect standard antidepressants to take 4 to 8 weeks, with sleep, appetite and energy often moving before mood. Some improvement by week 2 is a good sign, but its absence is not a final answer. About 4 weeks at a proper dose is the usual point to judge a drug, and full remission often takes 8 weeks or more. Esketamine, dextromethorphan-bupropion and zuranolone act faster, but each has a specific approved use.
Last updated: September 2026. This article is for informational purposes only and does not constitute medical advice. Talk with your prescriber before starting, changing or stopping any antidepressant.