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Selective serotonin reuptake inhibitors (SSRI) and serotonin/norepinephrine reuptake inhibitors (SNRI) are two types of medication used to treat depression. The biggest difference between an SSRI and an SNRI has to do with neurotransmitters. Experts believe that depression occurs when brain chemicals called neurotransmitters become unbalanced. Antidepressant drugs attempt to bring these neurotransmitters back into balance and alleviate the symptoms of depression.
Although the exact cause is not known, three neurotransmitters have been identified as being related to depression. Studies showed imbalances in dopamine, norepinephrine, and serotonin in patients with depression. An SSRI and an SNRI both affect absorption of serotonin, but an SNRI also affects norepinephrine levels in the brain.
Another difference between an SSRI and an SNRI is chronological. SSRIs were the first breakthrough drug for treating depression, and this type of medication is still widely used. SNRIs are more recent and may reflect more progressive research into the brain chemistry of depressed individuals.
Side effects can differ between an SSRI and an SNRI. Shared possible side effects include agitation, decreased sexual desire, drowsiness, dry mouth, erectile dysfunction, headache, insomnia, nausea, rash, sweating, and weight gain. Additional side effects associated only with SNRIs include constipation, heart palpitations, higher blood pressure, muscle weakness, and vision problems. These conditions only occur in some patients taking antidepressants.
Some comparisons indicate that SNRI drugs work better than SSRIs; however, this view is highly subjective. Antidepressant effectiveness differs widely from patient to patient, and it can take many weeks or months to find the best treatment for a given individual. One reason why an SNRI may be more effective than an SSRI is that it affects both serotonin and norepinephrine levels in the brain. Serotonin influences mood, and norepinephrine affects energy levels and alertness. By raising levels of both neurotransmitters, an SNRI may offer greater relief from the symptoms of depression.
Many of the most common antidepressant drugs are classified as either an SSRI or an SNRI, but all depression treatments differ in effectiveness. Medical research shows that what works for one person may not work for another. Mild depression that does not include anxiety or panic disorder frequently responds well to an SSRI. When depression comes with the added symptoms of anxiety or panic, an SNRI may be more appropriate because it focuses on multiple neurotransmitters.