How long do antidepressants take to work?

The 3 most common questions I get regarding antidepressants are 1) are they addictive; 2) how long do they take to work; and 3) do they cause weight gain? (See this post to answer if they are addictive, and this post to see if they cause weight gain).

Everyone wants their treatments to work; and for them to work quickly. Unfortunately, antidepressants will not work instantly. It’s usually a longer-term treatment response for most people. Here’s a graph showing a general representation of what to expect when starting a new antidepressant:

Acknowledgement: Our mental health professor in university (shout out to Dr David Gardner) used this type of graph to help illustrate this topic; and I’ve used it with patients ever since.

Side effects

Sadly, the first effects that are potentially seen are side effects. Luckily, many of these (e.g. nausea, upset stomach, diarrhea) usually subside with time. It’s important to be aware of this so you don’t get discouraged.

Other side effects can linger, and if you are experiencing any side effects that are bothersome (i.e. impact your quality of life) or won’t go away, you should speak to your healthcare providers.

First impact on symptoms

Studies have shown that some improvement can start as early as 1-2 weeks after initiating treatment. The key word is improvement. You shouldn’t expecting a return to “normal” that quickly; if at all. Antidepressants alone don’t always get you back to “normal”, but they have been shown to be helpful.

There is also some data to suggest that those who do see some improvement (at least 20% improvement) within the first few weeks are those most likely to respond well to the current drug and dose.

The most common symptoms where we see initial improvement are sleep problems and appetite problems. Initially you may not personally notice a difference, but anecdotally many patients have told me that it was their loved ones or those closest to them who first noticed improvements. I know for myself (I take antidepressants), my wife was one of the first people to notice a difference…even before I did!

Longer term impact

This is usually where we see the biggest impact on mood. At 4-6 weeks we should generally be seeing improvements, and they tend to achieve their peak effect at about 2-3 months. Don’t get discouraged if you don’t achieve a “level” that you are happy with. There are other options available to maximize the effect, such as increasing the dose, adding on another agent, or just trying a different drug altogether.


I think it’s very important to have realistic expectations when starting a new antidepressant (particularly if you’ve never taken one). In my experience, when people have unrealistic expectations they are more likely to be disappointed.

So, to recap:

1-2 weeks– Side effects most likely
– Initial improvements on sleep and appetite
– Potentially some minor improvements on mood
4-6 weeks– Side effects usually have diminished or resolved (if they will)
– More substantial improvements on mood
2-3 months– This is where we expect “maximal” impact from the current drug and dose

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Dan Landry

Daniel (Dan) Landry, founder of, is an infectious diseases pharmacist at the Dr-Georges-L.-Dumont University Hospital Centre in Moncton, NB, Canada.

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