Mental health
SSRIs
Selective serotonin reuptake inhibitors — First-line antidepressants also used for anxiety disorders.
Education and reference only. This is a plain-language class overview — it deliberately contains no doses. Always check the current Summary of Product Characteristics (SmPC), the BNF and your local formulary before prescribing or administering any medicine.
What it is
SSRIs are usually the first-choice medicines for moderate-to-severe depression and for several anxiety disorders. They are generally better tolerated and safer in overdose than older antidepressants.
How it works
They block the reabsorption of serotonin in the brain, increasing its availability at the synapse. The full mood effect typically takes a few weeks to develop, which is important to set expectations and maintain adherence.
In practice
In practice the first few weeks are the critical window: benefit lags but side-effects and, in younger people, a small rise in suicidal thoughts come early — so arrange an early review. Set the expectation that mood lifts over weeks, continue for an adequate period once well, and always taper rather than stop suddenly. Watch for interactions with other serotonergic drugs and, in older people, for low sodium.
Examples
Practical use
How to take it & use it well
- Take it at the same time each day. Some people find taking it in the morning helps, while others take it at night if it makes them drowsy, so see what suits you.
- Swallow it with water and you can take it with or without food, though taking it with food may ease early nausea.
- Keep taking it even if you do not feel better at first, as these medicines usually take a few weeks to work fully.
- If you miss a dose, take it when you remember the same day, but skip it if it is nearly time for the next one. Do not double up.
- Do not stop suddenly, as this can cause withdrawal effects such as dizziness, flu-like feelings and mood changes. Any stopping should be done gradually.
- Tell someone you trust and contact your doctor urgently if your mood worsens or you have thoughts of harming yourself, especially in the early weeks.
Common uses
- Depression
- Generalised anxiety disorder, panic disorder, OCD
- Post-traumatic stress disorder (selected agents)
Monitoring
- Mood, anxiety and any suicidal ideation, especially in the first weeks
- Response and tolerability before changing dose
- Sodium in older people (risk of hyponatraemia)
Weighing it up
Advantages & disadvantages
Advantages
- They are effective for depression and a range of anxiety conditions, and are often a first choice.
- They are generally safer in overdose than older antidepressants.
- They are usually taken once a day, which is convenient.
- Most people tolerate them well once any early side effects settle.
- They are non-addictive in the sense that they do not cause cravings, though they should still be stopped gradually.
Disadvantages
- They often cause nausea, headache or sleep changes in the first week or two before settling.
- They can affect sexual desire and function, which can persist while taking them.
- They take several weeks to reach full effect, which can be frustrating.
- Stopping abruptly can cause unpleasant withdrawal effects, so they need tapering.
- There can be a short-term increase in agitation or, rarely, suicidal thoughts when starting, especially in younger people.
Key safety principles
What to watch for
- A small, recognised increase in suicidal thoughts can occur early in treatment, particularly in younger people — review closely after starting.
- Do not stop abruptly — taper to avoid discontinuation symptoms.
- Risk of serotonin syndrome if combined with other serotonergic drugs.
- Some agents prolong the QT interval; some increase bleeding risk, especially with NSAIDs or anticoagulants.
Key interactions
What to avoid or check alongside
- Combining them with other medicines that raise serotonin, such as certain migraine treatments, other antidepressants or tramadol, can cause a dangerous reaction called serotonin syndrome.
- Taking them with anti-inflammatory painkillers (NSAIDs), aspirin or blood thinners increases the risk of bleeding, particularly in the stomach.
- St John's wort should not be taken with them as it adds to serotonin effects.
- Alcohol can worsen drowsiness and low mood and is best limited.
- Some of these drugs can interact with other medicines that affect the heart rhythm.
- They can interact with certain other medicines broken down by the liver, so always share your full medication list.
Patient & carer advice
- It can take 2–4 weeks to feel the benefit — keep taking it
- Do not stop suddenly; speak to your prescriber about tapering
- Report worsening mood or thoughts of self-harm promptly
Use with
Related clinical calculators
Dose and risk decisions for this class often depend on renal function, weight or bleeding/stroke risk. These tools help:
Answers
SSRIs: frequently asked questions
How long until I feel better?
Some early changes may appear within a couple of weeks, but the full benefit usually takes several weeks. Keep taking it and stay in touch with your doctor during this time.
Can I drink alcohol with it?
Alcohol can worsen drowsiness and low mood and may reduce how well the medicine works, so it is best to limit or avoid it, especially when starting.
Can I stop it suddenly?
No. Stopping abruptly can cause withdrawal effects such as dizziness and flu-like symptoms. When the time comes to stop, your doctor will reduce it gradually.
Will it affect my contraception?
SSRIs do not generally reduce the effectiveness of hormonal contraception. If you have concerns, your pharmacist can confirm based on your specific medicines.
Is it safe in pregnancy?
Some SSRIs can be used in pregnancy when the benefits outweigh the risks, but this needs an individual discussion. Do not stop suddenly. Speak to your doctor if you are pregnant or planning to be.
Authoritative sources
Always verify against the source
This overview is for orientation. For doses, interactions, contra-indications and the full monograph, use:
Need a custom medicines or prescribing resource?
We build evidence-led clinical references, calculators and decision aids for teams.