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Serotonin and Noradrenaline reuptake inhibitors (SNRIs)

Duloxetine and Venlafaxine are two medications that may be appropriate for the right patient after a clinical assessment by your pain team. These medications are in a group called “Serotonin and Noradrenaline reuptake inhibitors,” or SNRIs for short. These medications were originally designed to treat depression and anxiety – and you may find that it says ‘depression or anxiety’ on the box.

But these are not the primary reasonswe use these medications in pain medicine. We know that when someone experiences pain, there are several body systems involved. While there are some neurotransmitters in our body that worsen pain experience (some ofthese are called glutamate, substance-P and CGRP), there are other neurotransmitters that can dampen or reduce pain.

Serotonin, and particularly noradrenaline, are two neurotransmitters that research suggests can help reduce pain. We also know that some people experiencing pain for more than 12 weeks start to produce less of these helpful neurotransmitters. Unfortunately, there is no blood test to know if you are deficient in these neurotransmitters or not. So, if you are deficient, these medications may help. If you are not deficient, then they are less likely to be helpful.

We know that if we give duloxetine or venlafaxine to four people with pain (particularly nerve-type pain), then one of those people will get areduction in pain of more than 50%. Others may get the lesser benefit, and some may have no benefit at all. This is why we may suggest you try one of these medications to see if it works for you. If it does not work, then we suggest reducing and ceasing it again. If it does work, then you can decide if it works well enough that you are happy to continue taking the medication, but our job is to give you the education and power to make these decisions yourself and weigh up the benefits and negatives.

While there are often benefits, there can be side effects. Commonly people experience nausea for the first few days when taking the medication – but this often settles by the end of one week. Other people may experience sleep changes – more or less sleep. This often also settles. These medications are classed as weight neutral – however, as everyone is different, some people may gain or lose small amounts of weight.

If you decide to try the medication, you need to give it 4-6 weeks to work. As it very slowly increases the serotonin andnoradrenaline in your body synapses (the nerve connections), you need to let it do its work. Often, we need to go up in dose at ~4 weeks to get a better response. For example, with duloxetine, most people get benefits between 60-120 mg, but we start at 30 mg to ensure people are comfortable with the medication and any side effects are minimized. If you have further questions, there is more information below and please feel free to discuss this further with your pain team or your GP.

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