Is my antidepressant working?
Three weeks in and underwhelmed? By the NHS’s own timeline, you are in the middle of the process — not at the end of it.
At some point around week three, almost everyone asks the same question, usually at night, usually of the ceiling: is this doing anything?
It is a fair question and a genuinely hard one, for a reason that has nothing to do with you being bad at introspection. You are trying to measure a change using the one instrument that is itself being changed. Mood colours memory — when you feel low, low is what you can most easily recall, and last month gets repainted in today's shade. Almost nobody can see their own slope while they are standing on it.
So the honest answer to “can I tell?” is: not reliably, not from the inside, not yet. Which is frustrating, and also worth knowing, because it stops you drawing a conclusion from evidence that was never going to be good enough.
At three weeks, you are not late
Before anything else, the timeline is worth knowing, because most people are measuring against one they have invented.
The NHS puts it plainly: antidepressants “usually take 1 to 2 weeks to start having an effect and can take up to 8 weeks to work fully.”1 Read that twice, because there are two different numbers in it, and the gap between them is where almost all the anxiety lives. Starting to have an effect and working fully are weeks apart. If you are three weeks in and underwhelmed, you are not a failed case. By the timeline your own health service publishes, you are in the middle of the process.
That is also why your doctor may want to see you every week or two at the start1 — not because something is expected to go wrong, but because this stretch is genuinely hard to read from the inside.
What that gap feels like is rarely dramatic. People describe it less as happiness arriving and more as the volume coming down slightly on the noise — an evening that ends sooner than it used to, a page you actually finish. It is easy to dismiss that as nothing. It is worth writing down instead, because it is exactly the kind of change memory discards.
Look at what you did, not how you felt
If the feeling is an unreliable narrator, use behaviour instead. Behaviour leaves a trace.
Did you reply to a message you would have left unread a month ago? Did you leave the house on a day you would normally not have? Did an evening feel shorter than it used to? Did you cook rather than not eat? Did you get through a phone call without rehearsing it first?
These are unglamorous, and that is exactly why they are useful — they do not depend on your mood to be recorded accurately. “I went out on Saturday” is true whether or not Saturday felt good.
Why a record settles it
This is the part where writing things down stops being a chore and starts being the only thing that actually answers the question.
If you have been logging your mood and doing the weekly check-ins, the change becomes visible in the one form your memory cannot distort — a line going somewhere over eight weeks. It is remarkably common to look back and find that the version of you from three weeks ago was, on paper, in a worse place than the version reading the chart, while feeling certain that nothing had changed at all.
It also gives you something to take to the review appointment other than an impression. “I think maybe slightly better?” is hard for a prescriber to work with. A trend, plus the date the dose changed, is not.
If you are using Nagi, that is what the doctor report is for — it puts the timeline, the direction and the medication history on one page. But the tool matters far less than the habit; a note on your phone every few days does most of the work.
When “not working” is worth saying out loud
Sometimes it genuinely is not working, and that is information, not failure. Improvement that starts and then stalls is a real thing, and it is worth naming rather than quietly tolerating for another six months on the grounds that you are being difficult.
The NHS is direct about this: if you “do not feel your medicine is helping you, talk to your doctor.”1 That is an instruction, not a favour you are asking for.
And being able to say “I am about seven weeks in, sleep steadied around week three, but my mood has not followed and I am still not functioning at work” is a far more useful sentence than “I do not think it is helping.” The first one tells your prescriber where you are. The second one tells them almost nothing.
The two versions of stopping
There are two crossroads where people stop taking antidepressants without telling anyone, and they arrive from opposite directions.
The first is nothing is happening, so what is the point — usually in the hard middle stretch, where side effects have shown up and benefit has not. The second is I feel much better now, so I do not need these — which is the medication doing its job, being read as evidence it is not needed.
Both of those are conversations to have with your prescriber, not decisions to make alone at 11pm. The NHS guidance is unambiguous: “Do not stop taking an antidepressant suddenly or without talking to your doctor first.”1 Withdrawal effects can begin within days and last for weeks — and they can feel enough like your depression returning to be mistaken for it, which is precisely why stopping is a decision made with a plan rather than on a bad Tuesday.
Ask. Nobody will be annoyed with you for asking.
The short version
You probably cannot tell yet, and that is expected — the published timeline runs to eight weeks. Watch what you did rather than how you felt, because behaviour leaves a trace and mood does not. Write some of it down, because in eight weeks the record will answer a question your memory cannot. And take the answer, whatever it is, to the person who prescribed it.
— Richard MacLean
Next: how long antidepressants take to work, and keeping track of medication changes.
Sources
- NHS, Overview — Antidepressants. nhs.uk — accessed 10 August 2026.
Nagi is a mental health companion, not a medical device, and nothing here is medical advice. Never start, stop, or change the dose of a prescribed medication without talking to your prescriber.