Medicines for depression: antidepressants

Antidepressants are medicines used to treat depression. The decision to take an antidepressant, undertake psychological therapy, or combine both approaches, is very individual. Talk to your doctor about what you think will work best for you.

Individual antidepressants can be grouped into different classes or groups, according to how they work chemically in the body. Within each group, there are usually several medicines which work in a similar way but may differ slightly from each other.

The different groups of antidepressants are about as effective as each other overall, but some people will respond to one antidepressant better than another. The type and severity of side effects can also be quite different between these groups of antidepressants. See How do the side effects of different antidepressants compare?

10 things you should know about antidepressants

1. You might need to try more than one
You might need to try more than one antidepressant before you find the one that suits you best — not everyone responds the same way to a particular antidepressant.

2. They take a while to work
Often you will start to feel better within 1 to 3 weeks of starting an antidepressant, but it can take 6 to 8 weeks to feel the full effect.

3. Some side effects are temporary, others are not
All antidepressants have side effects; some might go away after a few weeks (e.g. insomnia, nausea, dizziness), while others may not (e.g. sexual problems).

4. Talk to your doctor if you have side effects
If you find you cannot put up with the side effects of your antidepressant, talk to your doctor about trying a lower dose or switching to a different antidepressant. A psychological therapy, such as CBT, could also be an option.

5. Take the full course to keep depression away
Keep taking your antidepressant after you start to feel better for as long as your doctor advises (usually 6 to 12 months) — this will reduce the risk of your depression coming back when you stop treatment.

6. Don't stop suddenly
With most antidepressants, stopping them suddenly can cause symptoms such as dizziness, nausea or feeling jittery. When it’s time to stop taking your antidepressant, your doctor will usually need to reduce the dose gradually over at least a few weeks. Your doctor can work out a dose reduction plan that is right for you and your medicine.

7. Know which medicines interact
Some antidepressants increase the amount of serotonin (a neurotransmitter or brain chemical). Combining these antidepressants with other medicines or illegal drugs that also increase serotonin can cause a serious reaction called serotonin syndrome or serotonin toxicity. See What is serotonin syndrome? for combinations to avoid. Also see the antidepressants A-Z for links to individual antidepressant pages listing other interactions.

8. Try psychological therapy first for mild depression
For mild depression, it’s better to try psychological therapies first, because they are more effective than antidepressants in this situation.

9. The effects of CBT last longer
Cognitive behavioural therapy (CBT), a talking therapy, is about as effective as antidepressants for moderate depression, but the benefits may last longer.

10. Severe depression should be treated with an antidepressant
Antidepressant therapy is advisable if you have severe depression; psychological therapies may be useful once you start to feel better.

How do antidepressants work?

Serotonin is one of the neurotransmitters (brain chemicals) that transmit signals between cells in your brain. Serotonin, along with other neurotransmitters such as noradrenaline and dopamine, are thought to have an important effect on your mood. Different neurotransmitters control different functions — often more than one. The role of neurotransmitters in causing depression is not fully understood.

Antidepressants increase the amount of certain neurotransmitters, and this is how they are thought to reduce the symptoms of depression.

How effective are antidepressants?

About 50% of people taking antidepressants find their depression symptoms are halved. Antidepressants reduce symptoms such as:

  • feeling sad, hopeless or worthless
  • feeling excessively guilty
  • feeling suicidal
  • sleep problems (insomnia)
  • problems doing your usual work or hobbies
  • difficulty concentrating
  • restlessness
  • anxiety
  • loss of appetite.

Antidepressants are more effective for reducing symptoms in people with moderate or severe depression, rather than mild depression. Psychological therapies, such as CBT, are more effective than antidepressants for mild depression, and about equally effective for moderate depression, although the effects of CBT may last longer. Antidepressant therapy is advisable if you have severe depression; psychological therapies may be useful once you start to feel better.

As with all medicines, there is a placebo effect with antidepressants — this means some people who took a placebo (an inactive, or sugar, pill) in clinical trials also felt better. In trials of antidepressant use, about 30% of the placebo group found their symptoms were halved. This doesn’t mean antidepressants don’t work — but suggests there are several factors involved.

Placebos can have an effect because of the expectation of getting better, and because of other factors such as talking to the staff running the clinical trial. It may also be that some people improve over time anyway, regardless of treatment. This could be the case particularly with trials which recruited people with mild depression. Read more about placebos and clinical trials.

For more information

  • Malhi GS, Parker GB, Greenwood J. Structural and functional models of depression: from sub-types to substrates. Acta Psychiatr Scand 2005;111:94–105.;jsessionid=653DA568E96E2A126D014A4E1C5AC5B4.d01t04 (accessed 22 February 2012).
  • Williams JW Jr, Mulrow CD, Chiquette E, et al. A systematic review of newer pharmacotherapies for depression in adults: evidence report summary. Ann Intern Med 2000;132:743–56. (accessed 22 February 2012).
  • National Collaborating Centre for Mental Health. Depression: the NICE guideline on the treatment and management of depression in adults (updated edition). London: National Institute for Health and Clinical Excellence, 2010. (accessed 9 February 2012).
  • Psychotropic Expert Group. Therapeutic Guidelines: Psychotropic, Version 6. In: eTG complete [Internet]. Melbourne: Therapeutic Guidelines Limited; 2008. (accessed 9 February 2012)
  • Rossi S, ed. eAMH [online]. Adelaide: Australian Medicines Handbook, 2012. (accessed 22 February 2012)