How are SSRIs and SNRIs different?

Question

How does each work and why might one be prescribed over the other?

Answer 1

Both selective-serotonin reuptake inhibitors (SSRIs) and serotonin-norepinephrine reuptake inhibitors (SNRIs) treat depression, as well as other conditions such as anxiety and obsessive-compulsive disorder.

Reuptake inhibitors prevent reuptake into the synapse. Your brain has neurons and synapses. There is a presynaptic neuron, a synapse, and a postsynaptic neuron. The neurons are like gates. The synapse is the space in between gates.

One theory about conditions like depression and anxiety is that the molecules of serotonin and norepinephrine get pulled back into the presynaptic neuron, the first gate, before they can cross to the postsynaptic neuron, the second gate. Getting "pulled back" is called reuptake, and means that the molecule cannot go onto different areas of the brain and cannot go do its job in those other areas. In people without these conditions, enough molecules can cross to the second gate and avoid being pulled back. People with these conditions need more help, and this is where reuptake inhibitors help.

Reuptake inhibitors give molecules more time to hang out in the synapse, the space between gates, to give it more time to go to the postsynaptic neuron. SSRIs prevent the reuptake of serotonin, and SNRIs prevent the reuptake of serotonin AND norepinephrine. Why are there two different medications?

Side effects vary from individual to individual, but SSRIs work on one molecule and tend to have fewer side effects, versus SNRIs, which work on two molecules and have more side effects for more people. Those who need these medications need to communicate with their doctor about how these medications are affecting them, and which medication is right for them. :)