What Do SNRI's Do?

Question: I read on your site that people that suffer from anxiety have increased serotonin, and SSRI’s reduce the amount of serotonin in the body. I suffer from GAD that manifests itself with my racing heart rate.
I have been taking Effexor now for about 3 weeks, and it seems like my heart rate has decreased. But I am still thinking the norepinephrine is going to keep my heart rate high. So, I was wondering, do SNRI’s reduce the amount of serotonin and norepinephrine?

— Ryan
Answer: SNRI stands for Serotonin & Norepinephrine Reuptake Inhibitor. SNRI’s initially increase synaptic serotonin and norepinephrine, but over time, they down regulate both systems (especially in anxiety disorders where both systems are upregulated). In conditions or areas of the brain where activity is too low, the SNRI can increase activity of serotonin and norepinephrine. In this sense, reuptake inhibitors can be thought of as modulators.
The degree to which norepinephrine is regulated by Effexor is dependent on dose. At 37 to 75 mg per day, norepinephrine effect is probably not clinically significant. At 150 mg norepinephrine activity is significant, and at 225 mg it’s probably equal in effect to the serotonin modulating effect.
Serotonin can also increase heart rate. Modulating serotonin and norepinephrine should help assuming that GAD is the cause of the rapid pulse.

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