SSRI
Meaning of SSRI: The word selective refers to serotonin alone, which is what separates this class from antidepressants acting on several messengers at once.
Definition of SSRI
An SSRI, or selective serotonin reuptake inhibitor, is a class of antidepressant that blocks the reabsorption of serotonin by the nerve cells that released it, leaving more of that chemical messenger in the gaps between cells. Medicines in the class are prescribed for depression and for several anxiety related conditions, and they are taken on a continuing daily basis.
How does blocking reuptake change anything?
Nerve cells do not touch. A signal crosses the narrow gap between them, called a synapse, when one cell releases a chemical messenger that binds to receptors on the next. Serotonin is one such messenger, involved in mood, sleep, appetite and pain perception. After release, most of it is pulled back into the cell that sent it by a transporter protein and stored for reuse, a recycling step called reuptake. An SSRI sits on that transporter and slows it, so serotonin lingers in the synapse and acts on the receiving nerve cell for longer.
That much happens within hours of the first dose, yet the effect on mood takes considerably longer, which tells against a simple shortage of serotonin as the whole explanation. The current understanding is that the sustained rise gradually changes receptor sensitivity and signaling downstream, and those slower adaptations track better with when people report improvement.
How do SSRIs compare with other antidepressants?
| Class | What it acts on | Examples |
|---|---|---|
| SSRI | The serotonin transporter only | Fluoxetine, sertraline, escitalopram, citalopram, paroxetine |
| SNRI | Serotonin and norepinephrine transporters | Venlafaxine, duloxetine |
| Tricyclic | Serotonin and norepinephrine, plus several unrelated receptors | Amitriptyline, nortriptyline |
| MAOI | The enzyme that breaks several messengers down | Phenelzine, tranylcypromine |
The narrower target is the reason the class became a common first choice for depression: it produces fewer of the effects that come from acting on unrelated receptors, which is what limited the older tricyclics.
What is known about starting and stopping?
Early effects and later benefit run on different clocks. Nausea, restlessness, sleep disturbance and sexual side effects tend to appear first and often settle, while the change in mood emerges over weeks. Stopping abruptly after a sustained course is associated with discontinuation symptoms such as dizziness, irritability and electric shock like sensations, which is a property of the class rather than a sign of addiction.
Also known as
Used in a sentence
The patient was started on an SSRI for treatment of moderate depression.
Good to know
SSRIs act specifically on serotonin reuptake, which distinguishes them from antidepressant classes such as serotonin and norepinephrine reuptake inhibitors that act on more than one chemical messenger.