Antidepressants – SSRIs

SSRI antidepressants are not just for depression

SSRI stands for selective serotonin reuptake inhibitor. They are a group of antidepressant medicines that are used to treat depression. They are also used to treat some other conditions such as bulimia, panic disorder, and obsessional-compulsive disorder.

How do SSRI antidepressants work?

Antidepressants alter the balance of some of the chemicals in the brain (neurotransmitters). SSRI antidepressants mainly affect a neurotransmitter called serotonin. An altered balance of serotonin and other neurotransmitters is thought to play a part in causing depression and other conditions.

How effective are SSRI antidepressants?

About 5-7 in 10 people with moderate or severe depression have an improvement in symptoms within a few weeks of starting treatment with an antidepressant. However, up to 3 in 10 people improve with dummy tablets (placebo) as some people would have improved in this time naturally. So, if you have depression, you are roughly twice as likely to improve with an antidepressant compared with taking no treatment. But, they do not work in everybody. As a rule, the more severe the depression, the greater the chance that an antidepressant will work well.

Note: antidepressants do not necessarily make sad people happy. The word ‘depressed’ is often used when people really mean sad, fed-up, or unhappy. True depression is different to unhappiness and has persistent symptoms (which often include persistent sadness). See separate leaflet called ‘Depression’ for more information about this condition.

The success rate of SSRI antidepressants can vary when used to treat the other conditions listed above (bulimia, etc).

How quickly do SSRI antidepressants work?

Some people notice an improvement within a few days of starting treatment. However, an antidepressant often takes 2-4 weeks to build up its effect and work fully. Some people stop treatment after a week or so thinking it is not helping. It is best to wait for 3-4 weeks before deciding if treatment with an SSRI is helping or not.

If you find that the treatment is helpful after 3-4 weeks, it is usual to continue. A normal course of antidepressants lasts at least six months after symptoms have eased. If you stop the medicine too soon, your symptoms may rapidly return. Some people with recurrent depression are advised to take longer courses of treatment.

When you are taking SSRI antidepressants

It is important to take the medication each day at the dose prescribed. Do not stop taking an SSRI medicine abruptly. This is because you may develop some withdrawal symptoms. The dose is usually gradually reduced before stopping completely at the end of a course of treatment. But don’t do this yourself – your doctor will advise on dosage reduction when the time comes. It is best not to stop treatment or change the dose without consulting a doctor.

Are there different types of SSRI antidepressants?

There are several different types. They include: citalopram, escitalopram, fluoxetine, paroxetine and sertraline. Each of these comes in different brand names. There is no best type that suits everyone. If the one chosen does not suit, it is sometimes necessary to change the dose, or change the preparation. Your doctor will advise. Also, if SSRI antidepressants do not help then another type of antidepressant may be advised.

What about side-effects and risks?

Most people have either minor, or no, side-effects. Possible side-effects vary between different preparations. The leaflet that comes in the medicine packet gives a full list of possible side-effects. You should read this before you start taking the medicine. It is beyond the scope of this leaflet to list all side-effects, but the following highlights some of the more common or serious ones.

As a rule, tell your doctor if a side-effect persists or is troublesome. Your doctor can advise on the best course of action – for example, to stop the medication, a switch to a different medicine, etc.

The most common side-effects

These include: diarrhoea, feeling sick, vomiting, and headaches. It is worth keeping on with treatment if these side-effects are mild at first as they may wear off after a week or so.

A possible sedating effect

SSRIs can cause a sedating effect (drowsiness) in some people. This side-effect is not common, and is not as much a problem as with some other types of antidepressants. However, you must be aware of the possibility, especially if you are a driver as it may impair your ability to drive safely. Any sedative effect is likely to be greatest in the first month of starting treatment, or on increasing the dose. The Driver and Vehicle Licensing Agency (DVLA) advises that you should not drive during this time if you feel that you are drowsy or sedated at all.

Bleeding into the gut

SSRIs are associated with a small increased risk of bleeding into the gut. This is especially in older people and in people taking other medicines that have the potential to damage the lining of the gut or interfere with clotting. Therefore, ideally, SSRIs should be avoided if you take aspirin, warfarin or non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen, naproxen, etc. If no suitable alternative to an SSRI can be found and you have an increased risk of bleeding then your doctor may advise that you take in addition another medicine to protect the lining of the gut.

Small increased risk of fractures

Research studies suggest that there is a small increased risk of fractures in people taking an SSRI. However, the reason for this increased risk is not clear.

Nervous system side-effects

Dizziness, agitation, anxiety, difficulty sleeping, and tremor have all been reported as possible side-effects.

Sexual problems

Problems with sexual function are a common symptom of depression. However, in addition to this, all antidepressants may cause some problems with sexual function. For example, problems getting an erection, vaginal dryness and decreased sex drive have been reported as side-effects in some people.

Antidepressants and suicidal behaviour

In recent years there have been some case reports which claim a link between taking antidepressants and feeling suicidal, particularly in teenagers and young adults. This may be more a risk in the first few weeks of starting medication or after a dose increase. It is debatable whether this possible risk is due to the medicine or to the depression. If it is due to the medication then the risk remains very small. And, overall, the most effective way to prevent suicidal thoughts and acts is to treat depression. However, because of this possible link, see your doctor promptly if you become increasingly restless, anxious or agitated, or if you have any suicidal thoughts – in particular, if these develop in the early stages of treatment or following an increase in dose.

Are SSRI antidepressants addictive?

SSRIs are not tranquillisers, and are not thought to be addictive. (This is disputed by some people, and so this is a controversial issue. If addiction does occur, it is only in a minority of cases.)

Most people can stop an SSRI without any problem. At the end of a course of treatment you should reduce the dose gradually over about four weeks before finally stopping. This is because some people develop withdrawal symptoms if the medication is stopped abruptly. If you have withdrawal symptoms it does not mean that you are addicted to the the medicine, as other features of addiction such as cravings for the medicine do not occur.

Withdrawal symptoms that may occur include: dizziness, anxiety and agitation, sleep disturbance, flu-like symptoms, diarrhoea, abdominal cramps, pins and needles, mood swings, feeling sick, and low mood. These symptoms are unlikely to occur if you reduce the dose gradually. If withdrawal symptoms do occur, they will usually last less than two weeks. An option if they do occur is to restart the drug and reduce the dose even more slowly.

References and Disclaimer | Provide feedback


  • Depression in adults, NICE Clinical Guideline (October 2009); Depression: the treatment and management of depression in adults
  • Depression, Clinical Knowledge Summaries (February 2010)
  • British National Formulary; 60th Edition (September 2010) British Medical Association and Royal Pharmaceutical Society of Great Britain, London (link to current BNF)


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