Serotonin and Norepinephrine Reuptake Inhibitors (SNRIs) are a class of Antidepressants that are used to treat several different mental health conditions, such as Depression and Anxiety.

SNRI antidepressants are the newest antidepressants, and are the second most-used class of antidepressants behind Selective Serotonin Reuptake Inhibitors (SSRIs). SNRIs are most effective when used alongside engaging in talking therapy.

There are only two types of SNRIs prescribed in the UK

Information on SNRI Antidepressants

It normally takes between four and six weeks for an antidepressant’s full effectiveness to be felt. However, some improvements may be visible after around a week.

It is important to take an antidepressant how and when a Doctor has advised. This involves taking the correct dose at the right time, and taking the medication on a consistent basis. Never take more than one dose at a time to make up for a forgotten dose.

A low dose is normally prescribed at first. This can be raised if needed. Once a person gets to the point where they are feeling healthy again, it is important to carry on taking the antidepressant for a bit longer, and then gradually withdrawing.

What conditions are SNRI Antidepressants used for?

SNRI antidepressants can be used for many different conditions. They are normally prescribed when a patient has failed to respond to an SSRI.

  • Depression
  • Anxiety
  • Trauma-related conditions
  • Obsessive-Compulsive Spectrum Disorders

What are the different types of SNRI Antidepressants?

There are only two SNRI antidepressants that are licensed for use in the United Kingdom for mental health conditions. Other SNRIs exist – such as Milnacipran (Ixel) – though these are not used for mental health.

  • Duloxetine (Cymbalta)
  • Venlafaxine (Efexor)

How do SNRI Antidepressants work?

It isn’t entirely known how SNRI antidepressants work. It is believed that antidepressants work by increasing levels of a group of chemicals in the brain called neurotransmitters.

SNRIs work on the neurotransmitters serotonin and at high doses – norepinephrine. These are chemicals that appear to be linked to mood. How the exact process works isn’t known.

In theory, as SNRIs target norepinephrine – unlike SSRIs – they should be superior. But in reality they appear to have the same effectiveness as SSRIs.

Side Effects of SNRI Antidepressants

Side effects are common with SNRI antidepressants. But, compared to other classes of antidepressants, SNRI antidepressants generally have milder side effects.

It is important to note that the side effects for each medicine within this class differs slightly. With any antidepressant, a Patient Information Leaflet will be included in the box. This leaflet provides an exhaustive list of side effects.

As mentioned, side effects from SNRI antidepressants are normally rather mild, and should only last for a few days as the body gets used to the medication. Some side effects, such as dry mouth or increased appetite, may be persistent.

Common side effects of SNRI antidepressants include headaches, sickness, drowsiness, dizziness, dry mouth, low sex drive and sexual dysfunction.

Serious side effects include suicidal thoughts, seizures, chest pain, psychosis or any abnormal behaviour. An overdose should be avoided, as it can cause the potentially fatal Serotonin Syndrome. If any of the side effects in this area appear, it is important to contact a Doctor or emergency department immediately. 

If side effects from antidepressants persist for a few weeks, or provide discomfort, it may be worth switching medication to an alternative antidepressant – although this should be done in conjunction with a Doctor.

Cautions of SNRI Antidepressants

It is important to thoroughly read the Patient Information Leaflet that comes with your medication. The leaflet will include specific cautions that should be taken into consideration when taking an antidepressant.

General considerations when taking antidepressants include:

  • Tell a Doctor about any medicine or substance that is currently being used – like any Herbal Remedies or CBD.
  • Avoiding alcohol in the first few days of treatment, to allow the body to get used to the medication. After adjustment is complete, it is advised to limit alcohol intake where possible.
  • Any antidepressant can react unpredictably with illegal drugs; therefore it is advisable to not use recreational drugs while using SNRIs.
  • Studies show that people under the age of 25 taking antidepressants are at a higher risk of suicidal ideation [1]. Therefore, it is important to exert caution during treatment.
  • Antidepressants shouldn’t routinely be taken during pregnancy or breastfeeding. It is important to discuss this with a Doctor.
  • Antidepressants are most effective when combined with a form of talking therapy. Antidepressants can help relieve symptoms, but not cure a mental health condition.


While SNRIs haven’t dislodged SSRIs like many people had expected, they are still a very effective class of antidepressants.

They have helped many people to see an improvement in their mental health. This is especially the case for many people that have struggled to see an improvement with an SSRI.

See Also



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[1] Leslie, L. K., Newman, T. B., Chesney, P. J., & Perrin, J. M. (2006). The Food and Drug Administration’s Deliberations on Antidepressant Use in Pediatric Patients. Pediatrics. 116 (1): p195-204. DOI: