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Antidepressant medicines explained

Both medicine and non-medicine treatments can help with depression and anxiety disorders, but no single treatment is right for everybody. Antidepressant medicines are also prescribed for other conditions such as bipolar disorder, bulimia, diabetic neuropathy and neuropathic pain. It’s important to find a treatment that works for you, and this may take some time. 

6 min read

How do antidepressant medicines work?

The decision to take an antidepressant, undertake psychological therapy, or combine both approaches, is very individual. Talk to your health professional about what you think will work best for you.

Antidepressant medicines change the levels of specific chemicals in the brain. These brain chemicals are alsocalled neurotransmitters.

Serotonin is one of the neurotransmitters 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 mood and anxiety. 

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

For depression, 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. 

For anxiety disorders, the evidence is a little different and suggests that some antidepressants may have more benefits than other antidepressants. Your doctor can advise you on which antidepressants might work best for treating your anxiety disorder.

How effective are antidepressants?

Depression

About 50% of people with depression who take an antidepressant find their depression symptoms are halved.

Antidepressants are more effective for reducing symptoms in people with moderate or severe depression, rather than mild depression. Psychological treatments, such as cognitive behavioural therapy (CBT), are more effective than antidepressants for mild depression, and about equally effective for moderate depression, although the effects of CBT may last longer.

In clinical trials studying the effects of antidepressants, some people who took a placebo (an inactive, or sugar pill) also felt better – about 30% of the placebo group found their symptoms were halved.

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 that recruited people with mild depression.

Anxiety

Studies have shown that about 50% of people with an anxiety disorder who take a type of antidepressant called a selective serotonin reuptake inhibitor (SSRI) get better. CBT and SSRI medicines are both effective in treating anxiety disorders. However, SSRIs are usually recommended after a trial of CBT or if the person being treated prefers medicines. 

Which antidepressant?

If you and your doctor agree a medicine may be helpful, you need to consider several factors when deciding which antidepressant may be best. It may take time, and trying more than one type of medicine, to find one that works best for you.

Your doctor will take other factors into account when prescribing an antidepressant, including possible side effects, any other illnesses you have, your age, and other medicines you take (some medicines can interact with each other). Being pregnant or breastfeeding are also important considerations.

For more information, see the Consumer Medicine Information (CMI) for your brand of medicine, available on our Medicine Finder page or from your pharmacist or prescriber.

Antidepressants: 10 things you should know

Types of antidepressants

Antidepressants can be grouped according to how they work. The different types are:

  • SSRIs: selective serotonin reuptake inhibitors: citalopram, escitalopram, fluoxetine, fluvoxamine, paroxetine, sertraline
  • SNRIs: serotonin and noradrenaline reuptake inhibitors: duloxetine, venlafaxine, desvenlafaxine
  • Serotonin modulator: vortioxetine
  • Noradrenaline reuptake inhibitors: reboxetine
  • TCAs (tricyclic antidepressants):  amitriptyline, nortriptyline, clomipramine, dothiepin, doxepin, imiprimine, trimipramine*
  • RIMAs (reversible inhibitors of monoamine oxidase A): moclobemide
  • Tetracyclic antidepressants: mianserin
  • Tetracyclic analogues of mianserin (sometimes called noradrenergic and specific serotonergic antidepressant [NaSSA]): mirtazapine
  • MAOIs (monoamine oxidase inhibitors): phenelzine, tranylcypromine
  • Melatonergic antidepressants: agomelatine*

* not available on the PBS.

Whether or not a medicine is available on the PBS for anxiety disorders may depend on the type of anxiety disorder needing treatment.

The type and severity of side effects can be quite different between the types of antidepressants, and between individual medicines of the same type.

Antidepressant medicine side effects  

Like all medicines, antidepressants can have side effects, so if you are considering them as a treatment option, talk to your health professional about which side effects are more important for you to avoid. 

Keep in mind that your own experience of side effects with a particular antidepressant may differ from that seen in clinical trials, and from other people’s experiences.

Some side effects are short-term

Some side effects of antidepressants might go away after a few weeks of taking them. This usually applies to insomnia (sleep problems), nausea (sickness in the stomach) and dizziness. Others, such as sexual side effects, are not likely to go away if you are affected by them.

Some people feel nauseated when they first start an antidepressant — taking it with food might help if you get this side effect. This nausea usually goes away after a few weeks.

If you are having trouble with side effects from your antidepressant, talk to your prescriber or pharmacist about how to manage them. A different antidepressant might give you less troublesome side effects.

For more tips on coping with antidepressant side effects, see Antidepressants: Get tips to cope with side effects on the Mayo Clinic website.

Antidepressants and suicide risk

Concerns have been raised about an increased risk of suicidal thoughts and acts when people first start taking antidepressants, or when they stop taking them. 

Suicidal thoughts and acts are a common symptom of depression and may also be associated with anxiety disorders. Often, someone is at their lowest point when they first start taking an antidepressant. It can also take a few weeks for an antidepressant to work. This makes it difficult to assess whether people who think about suicide when they first start taking an antidepressant do so because of the medicine or the underlying condition.

There may be a small increase in suicidal thinking or behaviour in children, adolescents and young adults when they first start taking an antidepressant. This risk is thought to be highest in people with depression and people under the age of 30 years. However, the overall risk is small and treating depression and anxiety disorders can prevent suicidal thoughts and behaviours.

Antidepressants have only a small role in treating children, and they should be used only under the supervision of a child psychiatrist. Antidepressants should only be prescribed for adolescents by doctors with training in this area, who are very familiar with the side effects, and are able to provide close monitoring for suicidal thinking, particularly in the first 4 weeks.

If you have any suicidal thoughts, get help straight away. It’s a good idea to write down an advance action plan with your health professional, for example, a list of five phone numbers to call; this allows some back-up in case you can’t get through to the first people you call. If you feel life is not worth living, get help immediately by calling:

  • Lifeline 13 11 14

If you are caring for someone starting treatment with an SSRI medicine, keep a close eye on them for worsening symptoms in the first few weeks, and call their doctor if you are worried.

Antidepressants and sexual side effects

You may get sexual side effects from your antidepressant, such as losing your sex drive, having difficulty reaching orgasm, or (for men) problems getting a strong erection.

It’s important to talk to your prescribing physician if you get sexual side effects, as these can be difficult to deal with and may not go away if you are affected by them. Your healthcare provider may be able to suggest a treatment option for you, for example:

  • Trying a different antidepressant – some antidepressants have a lower risk of causing sexual side effects than others, or
  • Reducing the dose of your antidepressant

If other strategies haven’t worked, taking an erectile dysfunction medicine may be an option for some men.

How long will I need to take antidepressants?

How long you will need to take antidepressants depends on the condition they are being used to treat.

With depression, you will start to feel better within 2 to 4 weeks of starting an antidepressant, but it can take 6 to 8 weeks to feel the full effect.

With anxiety disorders, it usually takes more time for an antidepressant to work. It may take 4 to 6 weeks before you start feeling better and it may take up to 12 weeks to feel the full effect of the antidepressant.

Regardless of the condition being treated, you should see your doctor at regular intervals to review your progress and discuss any issues related to treatment. If you are not improving, your doctor may discuss increasing your dose, switching to another antidepressant or referring you to another doctor or specialist.

If you are feeling better with antidepressant treatment you will usually need to keep taking it for a further 6 to 12 months to reduce the risk of your depression or anxiety disorder coming back. Having psychological treatment at the same time can further reduce the risk of your condition coming back. Some people may need to keep taking an antidepressant for a long time to prevent their symptoms coming back.

Stopping an antidepressant

If you and your doctor have decided it’s time for you to stop taking your antidepressant, you will usually need to reduce the dose gradually to avoid symptoms such as nausea, dizziness and feeling jittery, which are side effects from stopping antidepressants. How slowly you need to reduce the dose can depend on several factors, including the type of antidepressant, and how long you have been taking it.

In some cases, you need to slowly reduce the dose before you change to another antidepressant too.

Ask your doctor or pharmacist for advice on the best dose reduction plan for you.

Complementary medicines and antidepressants

There are many complementary medicines and alternative therapies for depression and anxiety disorders. Some have been tested in scientific clinical trials, but many have not. The Therapeutic Goods Administration (TGA) does not assess complementary medicines to check that they work.

It’s important to be open with your doctor about any complementary medicines you take, because some can interact with your other medicines.

See the following websites for information about complementary medicines and alternative therapies for depression:

6 min read

Date reviewed: 4 February 2019
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