SNRIs increase the availability of both serotonin and norepinephrine in the synapse. venlafaxine, duloxetine, and desvenlafaxine are the most commonly used. Clinical effect on anxiety usually develops over four to six weeks at an adequate dose. They're often chosen when an SSRI hasn't produced enough response, when fatigue is prominent, or when a co-occurring chronic pain condition makes the dual mechanism useful.
For plain-language detail on any specific medication, including what to expect week by week, side effects, and how to come off it, see our sister publication PsychiatryRx.
Selective serotonin reuptake inhibitors get most of the attention in conversations about anxiety medication, because they're usually tried first. Serotonin-norepinephrine reuptake inhibitors are the close second option and have a real place in anxiety treatment. The differences between the two classes are smaller than the names suggest and matter in specific situations.
What an SNRI is
An SNRI is a medication that increases the availability of two neurotransmitters in the synapse: serotonin and norepinephrine. The three most commonly used in anxiety are venlafaxine, duloxetine, and desvenlafaxine. Venlafaxine has the strongest evidence base for anxiety disorders, particularly generalized anxiety disorder, panic disorder, and social anxiety disorder. Duloxetine is also FDA-approved for generalized anxiety disorder, and is used widely in patients who have overlapping chronic pain conditions.
The mechanism is similar to SSRIs at the serotonin transporter, with an added effect on the norepinephrine transporter that grows more pronounced at higher doses. At low doses, venlafaxine in particular behaves more like an SSRI. The norepinephrine effect comes in as the dose increases.
How SNRIs feel
The subjective experience on a working SNRI tends to resemble the experience on a working SSRI. The same kinds of changes appear. Worry softens. Sleep often improves. The space between trigger and reaction widens. Most patients on a working SNRI describe the medication as not very noticeable in any direct way; what they notice instead is that situations which used to trigger a stress response stop landing as hard.
A few features distinguish the experience. Some patients notice a small lift in energy on an SNRI that they didn't get from an SSRI, related to the norepinephrine effect. Others notice a mild increase in heart rate or blood pressure at higher doses, which is monitored at follow-up visits. Discontinuation can be more difficult with venlafaxine than with most SSRIs, which is why tapering off is done gradually and under clinician guidance.
When an SNRI is chosen
A psychiatrist tends to consider an SNRI in a few situations.
When an SSRI has been tried at a therapeutic dose and hasn't produced an adequate response. Switching to a different class is a reasonable next step.
When fatigue is a prominent symptom alongside anxiety. The norepinephrine component can help with energy in a way that SSRIs don't consistently produce.
When there's a co-occurring chronic pain condition. Duloxetine has good evidence in fibromyalgia, chronic low back pain, and diabetic neuropathy, and using one medication to address both anxiety and pain can simplify the regimen.
When a patient has had a positive prior response to an SNRI. Prior response is a strong predictor of future response.
What to expect during the first few weeks
The first one to two weeks on an SNRI can include nausea, mild jitteriness, headaches, and changes in sleep. These are similar to what's seen with SSRIs and tend to settle. Most clinicians start at a low dose and increase gradually over the first few weeks to give the body time to adjust.
The clear therapeutic effect on anxiety usually develops over four to six weeks at an adequate dose. The dose required for anxiety often exceeds the starting dose by a meaningful margin, which is why a few dose increases are common before judging whether the medication is working.
What to know about stopping
SNRIs, particularly venlafaxine, can produce a distinctive set of discontinuation symptoms if stopped abruptly: dizziness, nausea, irritability, and a sensation sometimes described as electric shocks. These aren't signs of addiction. They're a withdrawal phenomenon that's usually avoidable with a slow taper. The taper is planned with the prescribing clinician and is generally done over weeks to months.
This isn't a reason to avoid SNRIs. It's a reason to discuss the eventual taper plan at the time the medication is started, so the long arc of treatment is clear from the beginning.
What doesn't change with an SNRI
The therapeutic decisions around an SNRI are the same as for any medication for anxiety. They're made with a clinician who knows the patient. They're reviewed at follow-up. They're paired, when possible, with psychotherapy or with behavioral changes that address the patterns the medication is helping to soften.
The medication is one part of a plan, not the plan itself.
Related: How CBT and SSRIs actually work for anxiety · What actually happens at a psychiatric visit · SNRI