Explains what antidepressants are, how they work, possible side effects and information about withdrawal.

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What are antidepressants?

Antidepressants are psychiatric drugs which are available on prescription, and are licensed to treat depression. Some are also licensed to treat other conditions, such as:

I took medication for six months. It helped lift the fog and gave me the energy I needed to tackle the root cause of my depression. There is no shame in taking medication to treat an illness.

How do they work?

All antidepressants work by boosting or prolonging the activity of particular brain chemicals, such as noradrenaline and serotonin, which are both thought to be involved with regulating mood.

Noradrenaline and serotonin are neurotransmitters. This means that they pass messages between nerve cells in your brain and also between nerves and other target organs in the rest of your body.

What different types of antidepressant are there?

There are several different types of antidepressants, which were developed at different times. They all tend to act on the same brain chemicals and cause similar effects, but the different types have different chemical structures, and may have different side effects.

The different types are:

(For a list of all antidepressants grouped by type see our page on comparing antidepressants, or for detailed information on an individual antidepressant see our antidepressants A–Z.)

Selective serotonin reuptake inhibitors (SSRIs)

About SSRIs:

  • They were first developed in the late 1980s, so they have been in use for about 30 years.
  • They work by blocking the re-uptake of serotonin into the nerve cell that released it, which prolongs its action in the brain.
  • The side effects SSRIs can cause are generally easier to cope with than those of other types of antidepressants.
  • They're the most commonly prescribed type of antidepressant in the UK.

Serotonin and noradrenaline reuptake inhibitors (SNRIs)

About SNRIs:

  • The first of these was developed in the early 1990s, so they're one of the newer types of antidepressant.
  • The're very similar in action to SSRIs, but they act on noradrenaline as well as serotonin.
  • They have a more selective action than tricyclics, which means they're better at targeting the brain chemicals which affect your mood without causing unwanted side effects by affecting other chemicals and other parts of the body as well.
  • They're sometimes preferred for treating more severe depression and anxiety.

Tricyclic and tricyclic-related drugs

About tricyclics:

  • They're the oldest type of antidepressant, first developed in the 1950s.
  • They work by prolonging the action of noradrenaline and serotonin in the brain.
  • They're called ‘tricyclic’ because of their chemical structure, which has 3 rings.
  • They tend to cause more unpleasant side effects compared with other types of antidepressants.

About tricyclic-related drugs: 

  • They act in a very similar way to tricyclics, but they have slightly different chemical structure.
  • They tend to cause more unpleasant side effects compared with other types of antidepressants, but they're less likely to cause antimuscarinic effects than tricyclics.

Monoamine oxidase inhibitors (MAOIs)

About MAOIs:

  • They work by making it harder for an enzyme (monoamine oxidase) that breaks down noradrenaline and serotonin to do its job, causing these chemicals to stay active in the body for longer.
  • They can have dangerous interactions with some kinds of food, so when taking MAOIs you need to follow a careful diet.
  • Because of these interactions, you're not likely to be prescribed an MAOI unless you've tried all other types of antidepressant and none of them have worked for you.
  • They should only be prescribed by specialists.

Other antidepressants

There are also several other antidepressants available which don't fit into any of the categories above.

This information was published in 2014. We will revise it in 2016.

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