A new study suggests that a single dose of one of the most popular antidepressants can rapidly alter the make-up of the brain. 

The changes can take place within a few hours, even though patients don't report effects until weeks later. 

Based on a new research published in the journal Current Biology, selective serotonin reuptake inhibitors (SSRI), a popular type of antidepressant, can change the way brain cells communicate with each other. Examples of SSRIs are Zoloft, Prozac, Paxil and Lexapro. 

"We show evidence that a single dose of a serotonin reuptake inhibitor dramatically alters functional connectivity throughout the whole brain in healthy subjects. Our network-centrality analysis reveals a widespread decrease in connectivity in most cortical and subcortical areas. In the cerebellum and thalamus, however, we find localized increases. These rapid and brain-encompassing connectivity changes linked to acute serotonin transporter blockade suggest a key role for the serotonin transporter in the modulation of the functional macroscale connectome," the report read. 

Serotonin, a chemical transmitter, has a multitude of functions, but is primarily involved in balancing mood. Antidepressants block the reabsorption of serotonin in the brain. 

According to the Los Angeles Times, the study's authors, who came from the Max Planck Institute in Leipzig, Germany, used a magnetic resonance imaging (MRI) machine to scan the brains of test subjects. The researchers were particularly interested in the differences between the connections in the gray matter of test subjects who took SSRIs and those who did not.

"We just tell them to let their minds wander and not think of anything particularly dramatic or upsetting," Dr. Julia Sacher, one of the authors of the study, said.

Researchers found that when serotonin was present, the functional connectivity decreased. However, there were parts where this was not the case. Two areas of the brain, the thalamus and the cerebellum, became more interdependent because of the drug. 

More research is required to explain this effect. The findings may help doctors better determine what antidepressant would best suit their patients. The researchers hope that the study would eventually help psychiatrists to use brain scans to find out whether patients respond to drugs or not.