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There are three main types of antidepressant medication:

    1) Tricyclics – These are the older drugs that have been available on prescription for over 20 years. They include amitriptyline, imipramine, nortriptyline and dothiepin. These are rarely used today, and only if there has been no benefit using some of the newer antidepressants.

    2) SSRI’s (Selective Serotonin Reuptake Inhibitors) – These are relatively recent drugs, that work just as well as tricyclics but tend to have fewer side effects. They include fluoxetine, sertraline , citalopram and es-citalopram.

    3) Newer variants have been introduced that have a more complex mechanism of action, such as venlafaxine, duloxetine and mirtazapine. These drugs have a broader range of biological actions.

    4) Mono-amine oxidase inhibitors – These are used less often and tend to be prescribed for patients who have not responded to other treatments. People taking these drugs must strictly avoid certain foods which may cause severe reactions. Newer drugs in this group do not require the same food restrictions.


Apart from treating depression, antidepressants are also used for treating other conditions such as anxiety and panic disorders, obsessive compulsive disorder and eating disorders.


The main side effects of the older tricyclic antidepressants are drowsiness, dry mouth and constipation. These side effects are uncommon with the newer antidepressants but they may produce nausea, restlessness and loss of appetite. In general, side effects are much worse at the beginning of treatment and get better after a few days, even if the dose is unchanged.

With older antidepressants, a low dose was often recommended at first, increasing gradually to a full dose. However this may delay the onset of the therapeutic effects. Most of the newer antidepressants are commenced already at a therapeutic dose, although further increases in dose are possible in case of insufficient improvement.

If you are concerned about side effects, mention this to your doctor before treatment starts, since it may affect his/her choice of antidepressant. Some antidepressants can stimulate the appetite so that you eat more and gain weight. This may be a good thing, but only if you are underweight when you start the course of treatment.


Antidepressants will usually start to lift mood and other symptoms of depression already in the first few days, but two to four weeks minimum are required to obtain the full beneficial effects. It is important to try to continue the course of treatment even if you have some of the side effects mentioned above.

If this is the first episode of depression, it is important to continue for 4-6 months after the symptoms are relieved, as studies have shown that chances of relapse are high if antidepressants are stopped immediately after an improvement in mood. The duration of treatment after the symptoms are relieved is even longer for patients with repeated episodes of depression, where it may be recommended that treatment with antidepressants be continued for 6-12 months or even years. If antidepressants are stopped earlier there is a risk that the symptoms of depression will resurface.


The response rate to most antidepressants is about 40-60%. This means that about 50% of people may not respond to their first choice of antidepressant. As there are several antidepressants on the market, another type of antidepressant can be tried if the first one does not work. This is also applicable to people who have to stop taking their medication due to side effects which they are not able to tolerate.

Research continues to discover better drugs with fewer side effects. Studies currently being carried out at the Institute of Psychiatry are looking into a way of predicting response to antidepressants based on the genetic profile of individuals, or to understand how antidepressants work. This study has built on earlier work that received financial support via the Psychiatry Research Trust.


Antidepressants should be stopped gradually over a period of weeks or months and under a programme set up by a doctor. Although antidepressants are not addictive, our bodies do get used to having them in the system, and so people may get side effects when they are stopped abruptly. Some people also get a recurrence of their depression when the tablets are stopped prematurely, so it is best for a doctor to monitor your mood in case treatment needs to be restarted or some other form of treatment is necessary.

If an antidepressant is stopped suddenly after regular administration for 8 weeks or more, one may experience reduced appetite or suffer from nausea, vomiting, headache, giddiness, chills or insomnia (such symptoms are known as discontinuation symptoms).

Stopping medication gradually over at least four weeks, with monitoring by a doctor, minimises the chance of getting discontinuation symptoms or a relapse into depression again.


Carmine M. Pariante, MD, MRCPsych, PhD
Professor of Biological Psychiatry and Head of the Sections of Perinatal
Psychiatry & Stress, Psychiatry and Immunology
Institute of Psychiatry, Kings College London, Department of Psychological Medicine

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