Soon depression sufferers may not have to wait weeks or months their antidepressant medication to kick in.

Scientists are closer to understanding how to develop fast-acting antidepressant medications after doing two studies on both humans and mice using the human and veterinary medication, ketamine.

Ketamine, which in recent years has been abused as an illegal “party drug,” probably won’t be used as antidepressant because it has too many side effects, researchers said.

The drug, however, relieves symptoms of depression within hours, rather than the weeks or months that it takes current antidepressants to work, and has given scientists a clue on how to develop medications that get to the biological root of depression.

The most recent study, from the National Institute of Mental Health (NIMH), backed up a previous study that showed ketamine blocks a receptor called NMDA on brain cells. But unlike the previous study, researchers this time learned that blocking this receptor increases the activity of another receptor, AMPA, which is crucial for ketamine’s rapid antidepressant actions.

“This new finding is a major step toward learning how to improve treatment for the millions of Americans with this debilitating disorder (and) toward eliminating the weeks of suffering and uncertainty they have to endure while they wait for their medications to work,” said NIH Director Elias Zerhouni, M.D., in a statement.

NMDA and AMPA are receptors for the neurotransmitter, glutamate, one of the chemical messengers that enable brain cells to communicate with each other. Glutamate has only recently been eyed as a factor in depression, according to the study, which was reported online in Biological Psychiatry on July 23. .

Researchers added that focusing on NMDA, AMPA and glutamate may allow for the development of drugs that quickly attack the root of depression, rather than taking the round-about approach that the currently available SSRI, monoamine oxidase inhibitor, and tricyclic antidepressants take.