Antidepressants are a group of medications that are used to treat depression.
What are antidepressants?
Antidepressants are medicines used to treat depression, anxiety and related conditions, such as eating disorders, obsessive-compulsive disorder and post-traumatic stress disorder. Antidepressants are also sometimes used to treat people with long-term (chronic) pain.
Antidepressants are effective for moderate to severe depression, but not very effective for mild depression. Psychological treatments such as cognitive behaviour therapy (CBT), talking therapy and regular exercise work better for mild depression. For children and young people with moderate to severe depression, the treatment chosen depends on how severe the depression is and personal preference.
For most people the effectiveness of antidepressants can be improved when they are used together with psychological therapies, like CBT, and lifestyle changes. Antidepressants work quickly in reducing symptoms, whereas CBT takes time to deal with the causes of depression and ways of overcoming it.
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What are the considerations when choosing an antidepressant?
The antidepressant medication you are prescribed will depend on the severity and type of your illness, if you have other medical conditions, if you are taking other medication, your response to antidepressant medication in the past and possible side effects.
Which antidepressants are available in Aotearoa New Zealand?
A variety of groups or classes of antidepressants is available in Aotearoa New Zealand. Each class works on different chemicals in your brain.
Class of antidepressant
Selective serotonin reuptake inhibitors (SSRIs)
Serotonin and noradrenaline reuptake inhibitors (SNRIs)
Can I use herbal supplements when taking antidepressants?
Some people find that herbal products like St John's Wort can be useful for depression but it can interact with antidepressant medicines. Before taking herbal supplements, check with your doctor or pharmacist if they interact with the medicine you are taking.
How do antidepressants work?
We don't know for certain, but researchers think that antidepressants work by increasing the activity of certain chemicals working in our brains called neurotransmitters. Certain neurotransmitters, such as serotonin and noradrenaline, are linked to mood and emotion.
While depression is not simply a deficiency of these chemicals, we do know that antidepressant medications help to relieve symptoms of depression and anxiety in approximately 50–70% of people who try them. Some people will respond to one antidepressant better than another so changes may be needed.
Neurotransmitters may also affect pain signals sent by nerves, which may explain why some antidepressants can help relieve long-term pain.
How long will I need to take antidepressants for?
This will depend on a number of factors and is best discussed with your doctor. It is common to be on antidepressants for at least 6 to 12 months. If you have recurrent depression you be advised to take them indefinitely.
- During the first few months of treatment, you'll usually see your doctor or a specialist nurse at least once every few weeks to see how well the medicine is working.
- If you are bothered by side effects or see little improvement in your symptoms after 6 weeks, talk to your doctor. They may change your dose or switch you to another antidepressant.
- If you plan to stop taking antidepressants, talk with your doctor first about how to do it safely. It's best to slowly decrease your dose. Suddenly stopping your antidepressant can cause side effects. It may also cause your depression to come back or get worse.
What about the side effects of antidepressants?
Different antidepressants have different side effects and risks. The most common side effects of antidepressants are usually mild. Side effects should improve within a few days or weeks of treatment, as your body gets used to the medicine.
- At the start of treatment: Some people can experience agitation and anxiety in the first few weeks of starting their antidepressant medicine. You may feel that your depression symptoms worsen at first because of the initial side effects. Keep in mind that things will get better and these side effects are likely to pass as your body gets used to the new medication. Tell your doctor if these effects are ongoing or troublesome.
- Do not stop taking your antidepressant medicine without checking with your healthcare provider. Stopping your medicine suddenly may make your symptoms worse.
- SSRIs: A few people experience sexual problems, weight changes or sleep problems when taking SSRIs. Read more about SSRIs.
- SNRIs such as venlafaxine have similar side effects to the SSRIs, and may also cause loss of appetite.
- Mirtazapine: Common side effects with mirtazapine include weight gain and drowsiness.
- TCAs: Side effects are more common with TCAs, and these can include drowsiness, blurred vision, weight gain, constipation and difficulty urinating (peeing), a dry mouth and sexual problems.
Let your doctor know if you experience any side effects while on antidepressants, so they can adjust the dose or try a different medication.
Did you know that you can report a side effect to a medicine to CARM (Centre for Adverse Reactions Monitoring)? Report a side effect to a product.
The use of antidepressants has been linked to an increase in suicidal thoughts and behaviour. Children, teenagers, young adults and people with a history of suicidal behaviour are particularly at risk. This is most likely during the first few weeks of starting an antidepressant or if the dose is changed. It is important to look for signs of suicidal behaviour such as agitation or aggression and ask about suicidal thoughts, self-harm, worsening of low mood. If you notice any of these signs, contact your doctor immediately.
It may be useful to tell a relative or close friend if you've started taking antidepressants and ask them to read the leaflet that comes with your medicines. You should then ask them to tell you if they think your symptoms are getting worse, or if they're worried about changes in your behaviour.
If you suspect you, or someone you know, might be suffering from depression, read more from our depression section or visit thelowdown.co.nz or depression.org.nz for helpful information, including a self-test.
The following links provide further information on antidepressants. Be aware websites from other countries may contain information that differs from Aotearoa New Zealand recommendations.
Antidepressants Royal College of Psychiatrists, UK
Antidepressants Patient Info, UK
Antidepressants – selecting one that's right for you Mayo Clinic, US
Depression – treatment options Option Grid
- The role of medicines in the management of depression in primary care BPAC, NZ, 2021
- Antidepressant drugs New Zealand Formulary, NZ
- Royal Australian and New Zealand College of Psychiatrists clinical practice guidelines for mood disorders. Australian and New Zealand Journal of Psychiatry, 2015
Additional resources for healthcare professionals
Switching antidepressants NZ Formulary, NZ
Depression overview National Institute of Clinical Excellence (NICE) Pathways
Assessment and management of depression in older adults BPAC, NZ, 2011