Serotonin and noradrenaline reuptake inhibitors, or SNRIs, are a relatively new type of medicine used primarily to treat depression in adults.
Three SNRIs are currently available in Australia. These are venlafaxine (brand name Efexor-XR), duloxetine (Cymbalta) and desvenlafaxine (Pristiq). They are all available as extended or controlled release tablets or capsules, which means that they only need to be taken once a day.
Some of the SNRIs are used to treat other conditions as well as depression.
Serotonin and noradrenaline are brain chemicals called neurotransmitters. These chemicals are involved in transmitting signals between nerve cells, and they are believed to have a role in regulating our mood and behaviour. Low levels of these brain chemicals are thought to be involved in causing depression.
The SNRIs block the reuptake (or recycling) of noradrenaline and serotonin into cells in the brain. This results in an increase in the levels of these two neurochemicals, which is thought to improve and elevate our mood.
Before you start taking an SNRI, it is important that you tell your doctor if you are taking any other medicines, including complementary medicines, or supplements. SNRIs can interact with several other medicines, including warfarin (Coumadin, Marevan), St John’s wort and other antidepressants. Interactions between medicines can cause reactions, which can at times be serious.
If you have been taking a different type of antidepressant or another medicine that also has an effect on the chemical serotonin, you will usually need to stop taking that medicine and wait at least two weeks before starting your SNRI. This is to prevent very high levels of serotonin accumulating in the brain, which can be dangerous. Your doctor will advise you when you can start taking the SNRI.
Medicines that have an effect on serotonin include:
Side effects of the SNRIs may include nausea, vomiting, constipation, dizziness, dry mouth and difficulty in sleeping. Some people have increased sweating and some have reported sexual problems. Often these side effects go away after a few days or weeks. Let your doctor know if you experience any side effects while taking your antidepressant.
Your doctor may monitor your blood pressure while you are taking an SNRI, as some people have had small increases in their blood pressure when taking these medicines.
If you have narrow angle glaucoma or raised intraocular pressure (raised pressure of the fluid inside the eye), your doctor will monitor you closely if your depression is treated with an SNRI.
Sometimes while taking antidepressants, particularly during the first few months of treatment, people may feel that their depression is worsening or they may have suicidal thoughts. If you do feel like this, or if you have any thoughts about death or suicide, talk to your doctor about this as soon as you can, or call one of the helplines noted in the box below.
Let your doctor know if you consume regular or large quantities of alcohol. People who drink large amounts of alcohol should not take duloxetine because it may interact with the alcohol and cause liver damage. People who already have liver disease should also not take duloxetine, as this medicine may worsen this disease.
You should avoid drinking alcohol if you are taking any of the SNRIs. This is the case with all medicines such as antidepressants that act on the brain, or central nervous system. Alcohol can worsen symptoms of depression, and it may interact with antidepressants to cause increased intoxication and drowsiness.
It is important that you tell your doctor if you are pregnant or planning to become pregnant. The SNRIs are not generally recommended to be taken during pregnancy because they may cause problems in the newborn baby. Withdrawal symptoms in the newborn are a possible risk when women take SNRIs during the last three months of pregnancy. Your doctor will discuss with you the risks and benefits of taking SNRIs if you are pregnant.
None of the SNRIs should be taken by women who are breastfeeding. This is because these medicines have been shown to be excreted in breast milk.
It is important that you don’t suddenly stop taking your antidepressant medicine without your doctor’s advice, as it is possible that this can result in withdrawal-like symptoms. These include nausea, headache, dizziness, lethargy and flu-like symptoms. To avoid this happening, when you have finished your treatment, your doctor will advise you how to gradually reduce the dose of the medicine over several weeks.
|If you or someone you know is depressed and/or having suicidal thoughts, see your doctor, or phone one of these helplines.|
|Lifeline (24 hours)||13 11 14|
|Kids Helpline (under 18 years of age)||1800 55 1800|
|Just Ask - rural mental health information||1300 13 11 14|
|Mensline Australia (24 hours)||1300 78 99 78|
|SANE Helpline - mental illness information, support and referral||1800 18 SANE (7263)|
Last Reviewed: 31 March 2010