Read the leaflet in the box and every side effect looks equally alarming, because they're printed in the same font. In practice they fall into three very different groups, and telling them apart is the single most useful skill you can have while taking psychiatric medication.
Group one: usually settles
Early, common, unpleasant, and generally easing over one to two weeks as the body adjusts. The NHS lists nausea, headaches, dizziness, dry mouth, drowsiness and difficulty sleeping among the common early effects of antidepressants; sedation and dizziness are common early with a lot of other psychiatric medicines too.
Riding these out is reasonable. Practical things that help: take it at the same time daily, ask your pharmacist whether yours can be taken with food, and if it's sedating ask whether the timing can move. What isn't reasonable is suffering in silence for three months because you assumed this was the deal.
Group two: does not settle on its own — but is fixable
These are the ones people quietly tolerate for years, or stop the medication over without ever mentioning them. Both are avoidable.
- Sexual side effects. Reduced desire, difficulty reaching orgasm, erectile problems. Extremely common with SSRIs and SNRIs, rarely raised, and a leading reason people stop taking medication without telling anyone. There are options.
- Emotional blunting. The lows lift, but so does everything else — you can't cry at a funeral or feel much at good news. A recognised effect worth reporting, not the price of being well.
- Weight gain and metabolic change. Significant with some antipsychotics in particular. Monitoring of weight, blood pressure, blood sugar and lipids should be happening — if nobody has checked, ask.
- Persistent sedation. If you're still sleeping through your alarm at week eight, that isn't settling.
- Movement effects — stiffness, tremor, or a restlessness you can't sit through. Report these; they are managed, not endured.
The rule of thumb: if a side effect is changing your life rather than your week, it's a group two problem and it needs raising.
Almost every side effect people stop medication over is one they never told the prescriber about.
Group three: ring today, or go to A&E
Rare. Recognisable if you know the pattern. This is the part worth actually remembering.
Signs of too much lithium in the blood
The NHS's own instruction for these symptoms is to call 999 or go to A&E now, and to stop taking lithium straight away. Take your medicines with you, and don't drive yourself.
- Stomach ache, feeling sick, diarrhoea
- Blurred vision
- Feeling very thirsty, needing to pee much more than normal, or losing control of pee or poo
- Feeling lightheaded or drowsy
- Confusion or blackouts
- Shaking, muscle weakness, twitches, jerks or spasms affecting the face, tongue, eyes or neck
- Difficulty speaking
This is the one and only place on this site that tells anyone to stop a medication, and it is the NHS's wording, not mine. Lithium levels can rise dangerously when you are vomiting, have diarrhoea, are dehydrated, are very hot, or start certain other medicines — which is why sick days matter on lithium.
A sore throat, fever or flu-like illness on clozapine
Contact your clozapine clinic or team the same day — you need an urgent blood test. Clozapine can rarely cause a severe drop in the white cells that fight infection, which is exactly why clozapine comes with mandatory blood monitoring. An ordinary-looking infection is the thing that must be checked, not waited out.
High temperature with muscle stiffness and confusion
Fever, marked muscle rigidity, confusion or altered consciousness, sweating and an unstable pulse or blood pressure — particularly after starting or increasing an antipsychotic. This pattern can indicate neuroleptic malignant syndrome. It is rare and it is a medical emergency. Call 999.
Agitation, sweating, shivering, twitching and a racing heart
Especially soon after a dose increase, or after another medicine was added — including over-the-counter remedies, some painkillers, and St John's wort. This pattern can indicate serotonin syndrome. Ring 111 urgently, or 999 if it is severe or getting worse quickly.
And these, whatever you're taking
- Any new rash — especially with lamotrigine, where a rash is taken extremely seriously and needs contact straight away.
- New or worsening thoughts of suicide or self-harm — particularly in the first weeks of a new medication, and particularly if you are 24 or under.
- Fainting, chest pain, or an irregular heartbeat.
- Yellowing of the skin or the whites of the eyes, or very dark urine.
- Difficulty passing urine, or a swollen painful abdomen.
- Swelling of the face, lips or tongue, or difficulty breathing — call 999.
Report it yourself: the Yellow Card scheme
You don't need a professional to report a side effect. The MHRA runs the Yellow Card scheme and patients, carers and the public can report directly at yellowcard.mhra.gov.uk or through the Yellow Card app.
It takes a few minutes, and it is not a complaint about your care — it's how safety signals get spotted. Several of the warnings in this post exist because enough people reported something that looked like nothing on its own. Report anything you suspect, even if you're not sure the medicine caused it. Uncertainty is expected; that's what the analysis is for.
How to raise a side effect and be taken seriously
- Name the medicine and when it started.
- Say what the side effect stops you doing, not just what it is. "I'm drowsy" gets less traction than "I can't drive to work and I've missed three shifts."
- Say whether you want it managed or want to change medication. Prescribers often can't tell which you're asking for.
- Ask what the alternatives are, and what the trade-off is with each.
- If you can't get through to the prescriber, ring your pharmacist. Same day, no appointment, and they know the interactions better than almost anyone.
Worth asking about any new medication
- Which side effects should settle, and by when?
- Which ones mean I ring you, and which mean 999?
- Does this need blood tests, an ECG or any other monitoring?
- What should I do on days when I'm vomiting or can't keep fluids down?
Common questions
Which psychiatric medication side effects are an emergency?
Call 999 for: fever with muscle stiffness and confusion (possible neuroleptic malignant syndrome); swelling of the face, lips or tongue or difficulty breathing; and the NHS's listed signs of lithium toxicity — vomiting and diarrhoea, coarse shaking, slurred speech, blurred vision, confusion or blackouts — for which the NHS says to stop lithium straight away and go to A&E. Ring 111 urgently for agitation with sweating, shivering, twitching and a fast heart rate, which can indicate serotonin syndrome. Contact your team the same day for a sore throat or fever on clozapine, any new rash, or new thoughts of suicide or self-harm.
How long do side effects last?
Early effects such as nausea, headache, dizziness and drowsiness usually ease over one to two weeks. Sexual side effects, emotional blunting, weight gain and persistent sedation generally do not settle on their own — those are worth raising, because they are often manageable.
Why does clozapine need blood tests?
Clozapine can rarely cause a severe fall in the white blood cells that fight infection. Regular blood monitoring is mandatory for that reason, and it is why any sore throat, fever or flu-like illness while taking clozapine needs an urgent blood test rather than a wait-and-see.
Can I report a side effect myself?
Yes. The MHRA's Yellow Card scheme takes reports directly from patients, carers and the public at yellowcard.mhra.gov.uk or via the Yellow Card app. You do not need to be certain the medicine caused it.
Should I stop the medication if I get a side effect?
Not on your own — with the single exception of the lithium toxicity symptoms above, where the NHS's own advice is to stop straight away and get emergency help. For everything else, contact your prescriber or pharmacist. Stopping abruptly can cause withdrawal effects and can allow the original illness to return.
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 lithium — signs of too much lithium in the blood — nhs.uk
- Side effects of antidepressants — nhs.uk
- Yellow Card scheme — reporting for patients and the public — mhra.gov.uk
- The Yellow Card scheme: guidance for healthcare professionals, patients and the public — gov.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.
One post a day, in plain English
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.