SSRI antidepressants

SSRIs are used to treat depression and many other conditions such as anxiety, obsessive-compulsive disorder (OCD) and post-traumatic stress disorder (PTSD). They are used in combination with psychological therapy or counseling.

Which SSRIs are available in New Zealand?

What conditions are SSRIs used for?

Although SSRIs are called antidepressants and are commonly used to treat moderate-to-severe depression, they are also used to treat many other conditions such as anxiety disorders (social anxiety, generalised anxiety, panic disorder, OCD and PTSD), eating disorders such as bulimia nervosa, and mood changes related to periods (menstruation) called premenstrual dysphoric disorder. 

We don't know for certain, but we think that SSRIs work by increasing the activity of certain chemicals working in our brains called neurotransmitters. They pass signals from one brain cell to another. The chemicals most involved in depression are thought to be serotonin and noradrenaline. SSRIs are the most frequently prescribed antidepressants. They are called selective because they only affect serotonin Read more about antidepressants. Read more about what to expect when starting SSRIs — see frequently asked questions (FAQs) about SSRIs. 

How to take SSRIs safely

SSRIs are usually taken once a day. Your doctor will start you on a low dose and if you need to, will increase your dose slowly. This allows your body to get used to the medicine and reduces side effects.

  • You can take your SSRI with or without food, but if you think it is upsetting your stomach, try taking it with food.
  • Keep taking your SSRI every day. It may take 4 to 6 weeks to notice the full benefits of the medication.
  • If you think it is not working for you, do not stop taking your SSRI suddenly; speak to your doctor or nurse before stopping. It is usually best to stop taking SSRIs slowly to avoid adverse effects.
  • Talk to your doctor if you have ever experienced mania, have epilepsy, heart disease or diabetes.
  • If you are pregnant, or wish to become pregnant, let your doctor know.


Avoid alcohol while you are taking SSRIs, especially when you first start treatment. Drinking alcohol while taking SSRIs can cause drowsiness and affect concentration, putting you at risk of falls and other accidents. It can also cause agitation, aggression and forgetfulness. If you do drink alcohol, drink only small amounts and see how you feel. Do not stop taking your medication.

What about side effects from SSRIs?

Like all medicines, SSRIs can cause side effects, but not everyone gets them. Often side effects improve as your body gets used to the medicine.

Common side effects

When you first start taking SSRIs, they can cause nausea (feeling sick), vomiting (being sick), having trouble sleeping (insomnia), sweating, anxiety or restlessness and diarrhoea (runny poos). Worsening of depression and suicidal thoughts can happen in the first few days or weeks of starting an SSRI. It is very important to talk to your healthcare provider if you have these feelings.

Suicidal behaviour

The use of antidepressants has been linked with 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 is ok and important to ask about suicidal thoughts and this will not increase risk. 

Sexual side effects

SSRIs in both men and women can cause reduced sexual drive, lack of libido and problems keeping an erection, and reduce the intensity of orgasm. It’s important to talk to your healthcare provider if you get these effects, as they can be difficult to deal with and may not go away. Your healthcare provider may be able to suggest treatment or may reduce the dose of the SSRI or change to a different one. Read more about medicines and sexual problems.  

Low sodium levels

SSRIs cause low sodium levels in your blood in up to one-third of people who take them, particularly in elderly people, women, people who are also taking diuretics (water tablets) or omeprazole and people with low body weight. Let your doctor know if you have signs of low sodium such as dizziness, confusion, agitation, cramps, unsteadiness, feeling faint or tired.

Serotonin syndrome

Serotonin syndrome occurs when the level of serotonin in your brain, gets too high. It can happen with the use of some medicines such as SSRIs, tramadol or herbal supplements. You are at risk of serotonin syndrome if you just started taking or increased the dose of your SSRI, or also take other medicines or herbal supplements that increase serotonin levels such as St John's Wort. Symptoms can range from mild such as shivering and diarrhoea (runny poos) to severe such as muscle rigidity, fever and seizures. Milder forms of serotonin syndrome may go away within a few days of stopping the medicines that caused your symptoms. Severe serotonin syndrome needs hospital admission and can be fatal if not treated. Read more about serotonin syndrome.

Risk of bleeding

SSRIs can increase your risk of bleeding especially if taken with NSAIDs (non-steroidal anti-inflammatory drugs) such as diclofenac and ibuprofen. Check with your doctor or pharmacist before you take pain relief.

Learn more

See frequently asked questions (FAQs) about SSRIs.

The following links provide further information about SSRIs. Be aware that websites from other countries may have information that differs from New Zealand recommendations.

SSRI antidepressants Patient Info, UK, 2016
Antidepressant medicines explained NPS MedicineWise, Australia, 2017


  1. Depression or distress? Examining SSRI prescribing in primary care BPAC, NZ, October 2019
  2. A primary care approach to sodium and potassium imbalance. BPAC, NZ, September 2011
  3. Serotonin syndrome: short time to onset, even with the first dose Medsafe Prescriber Update, NZ, March 2016 
  4. Sexual dysfunction associated with antidepressants and antipsychotics Medsafe Prescriber Update, NZ, March 2015 
  5. Can I have a drink with that? Medsafe Prescriber Update, December 2014 
  6. Selective serotonin re-uptake inhibitors New Zealand Formulary
  7. Royal Australian and New Zealand College of Psychiatrists clinical practice guidelines for mood disorders. Australian and New Zealand Journal of Psychiatry, 2015
Credits: Sandra Ponen, Pharmacist. Reviewed By: Angela Lambie, Pharmacist, Auckland Last reviewed: 07 Feb 2018