Here is the shape of the thing, and it is a cruel shape: with most antidepressants, the unpleasant effects turn up in the first few days and the useful effects turn up weeks later. So the honest description of week two is "I feel a bit sick, I'm sleeping badly, and I am no less depressed than I was."
That is not the medication failing. That is the medication behaving exactly as expected. But nobody tells people this, so they stop — and a drug that would have worked never gets the chance to.
Days 1 to 7: the settling-in period
Whatever you're going to get in the way of early side effects, this is usually when it shows up. The NHS lists nausea, headaches, drowsiness or difficulty sleeping, dizziness and dry mouth among the common ones. Some people feel jittery or wound-up for the first few days — more anxious, not less, which is disorientating when anxiety is the reason you're taking it.
Most of these ease over one to two weeks as the body adjusts. Knowing that they are expected, common and usually temporary is the difference between riding them out and panicking.
What is not in the "ride it out" category: new or worsening thoughts of suicide or self-harm, severe agitation you can't sit still through, or anything in the red-flag box below. Those get reported now.
Days 7 to 21: the point where most people quit
Week two and three are where the drop-out happens. The side effects have not fully gone, and the benefit has not yet arrived. There is nothing to show for the inconvenience.
This is the moment to have already made two decisions:
- You will not decide anything about this medication alone at 2am. Nothing about week two is a good basis for a permanent decision.
- If it becomes intolerable, you ring rather than stop. There are usually options — the timing of the dose, taking it with food, waiting a bit longer, or a different drug entirely. Stopping abruptly is the one route with no upside.
Weeks 3 to 6: the parts that shift first
When something does start moving, it usually isn't mood. Mood tends to be last. What tends to shift first is more mechanical:
- Sleep. Getting off to sleep, or stopping the 4am wake-up.
- Appetite. Food starting to be food again.
- The worst hour. Many people have a specific worst part of the day. It gets shorter before it gets less bad.
- Doing. You answer a message. You leave the house. You do it without the enormous negotiation it required last month.
Almost everybody underestimates this phase, because you cannot feel a gradient from inside it. You only see it by comparison — which is the entire argument for writing something down.
Two lines a day on your phone. Hours slept, and the worst hour rated out of ten. That is the whole diary, and at week six it will tell you something your memory cannot.
Weeks 6 to 8: the real review point
The NHS puts the full effect at up to eight weeks. So a fair conversation about whether this particular medication is doing its job happens somewhere around then — not at week two, and not at week twenty.
Bring the diary. "I don't think it's working" and "over six weeks my sleep went from four hours to six and a half, and the mornings are still bad" lead to completely different appointments. The second one gets you a decision. The first one gets you a shrug.
If it genuinely hasn't worked, that is common and it is not the end. Switching to a different antidepressant, or adding something alongside, is standard practice. The first one not working tells you very little about whether the second one will.
Report these straight away — don't wait for the review
- New or worsening thoughts of suicide or self-harm. The NHS is explicit that people aged 24 or under, or who have had these thoughts before, may be most at risk in the early weeks. This is a known effect, it is taken seriously, and reporting it is not an overreaction.
- Severe restlessness or agitation — a physical inability to keep still, sometimes with a feeling of dread. It has a name (akathisia), it is recognised, and it is not "just anxiety".
- Agitation with sweating, shivering, twitching muscles, a racing heart or diarrhoea, especially after a dose change or after another medicine was added. This can indicate serotonin syndrome and needs urgent advice — call 111, or 999 if severe.
- Palpitations or an unusually fast heartbeat.
- Any rash.
- In older adults especially: confusion, marked drowsiness, unsteadiness or a fall — low sodium is a recognised risk and is picked up on a blood test.
If someone's life is at immediate risk, call 999.
Alcohol, in one paragraph
Alcohol is a depressant, it wrecks sleep architecture, and it stacks with the sedating effects of a lot of psychiatric medication. It also, quietly, undoes much of what you're paying for in side effects. Nobody is going to pretend everyone abstains, and the right advice depends on the specific drug — some combinations matter far more than others. Ask your pharmacist about yours; it's free and takes two minutes.
Things worth doing in the first fortnight
- Set an alarm for the same time every day. Missed and doubled doses cause a surprising amount of the misery attributed to the drug itself.
- Tell one person you've started. Other people notice change before you do.
- Read the leaflet once, then put it away. Do not re-read it at midnight looking for symptoms.
- Book the follow-up now, at around six weeks, rather than waiting to see.
- Save your pharmacy's number in your phone. A pharmacist will answer a medication question the same day.
Worth asking when you're prescribed one
- Which side effects should I expect in the first week, and which ones mean I ring you?
- Is there a better time of day to take this, given how it affects sleep?
- When should we review it, and can that be booked now?
- Who do I contact if things get worse before then — you, the GP, or 111?
If you're already past this stage and thinking about coming off, read Day 3 before you change anything.
Common questions
How long do antidepressants take to work?
The NHS says antidepressants usually take one to two weeks to start having an effect and can take up to eight weeks to work fully. Sleep and appetite often improve before mood does.
I feel worse in the first week. Is that normal?
Early side effects such as nausea, headache, disturbed sleep and feeling jittery are common and usually ease within one to two weeks. Feeling more anxious for a few days is recognised. But new or worsening thoughts of suicide or self-harm, severe agitation, or a racing heart are not things to wait out — contact your prescriber, your GP or 111 the same day.
Should I take it in the morning or at night?
It depends on the drug and on how it affects you — some are sedating and some are activating. Your prescriber or pharmacist can tell you which yours is. What matters most is taking it at the same time every day.
What if it hasn't worked after eight weeks?
That is common and it is not the end of the road. Switching to a different antidepressant, or adding something alongside it, is standard practice. The first one not working tells you very little about whether the next one will. Bring a record of the eight weeks to that appointment — it makes the decision much easier.
This page names medicines but gives no doses and no instructions. It is written to help you have a better conversation with the person who prescribes for you — not to replace them. Do not start, stop, increase or reduce any medication because of something you read here. If something on this page worries you about your own treatment, ring your prescriber or your pharmacist, or call 111.
Sources checked for this page
- Side effects of antidepressants — nhs.uk
- Antidepressants — overview — nhs.uk
- Depression in adults: treatment and management (NG222) — nice.org.uk
Last reviewed: 20 August 2026. Next review due: February 2027.
Written by Dereck Tafuma, Registered Mental Health Nurse (NMC PIN held) and qualified teacher. Medicines guidance changes — if you find something out of date on this page, please tell me and I'll correct it.
This page is general information for the public. It is not personal medical advice, it contains no doses, and it cannot take the place of an assessment by someone who can actually see you. Nothing here is written on behalf of any employer.
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A daily series on psychotropic medication — what it does, what it costs you, what to ask, and what needs a phone call today. No doses, no recommendations, no drug company money.