Sheryl Smith studies a neurotransmitter that may be responsible for pre-menstrual syndrome

From CNN Health Correspondent Elizabeth Cohen

ATLANTA (CNN) -- One reason Sheryl Smith studies premenstrual syndrome is that she's experienced it personally.

"I usually find that things that are annoying annoy me more during that time of the month, and it does seem to be a pattern," she said. "I've talked to other women and a lot of them report the same thing."

For years doctors said PMS was just psychological.

"Being a woman, I can really understand that something like this is real," Smith said. "It's not just something that's due to psycho-social factors or is imagined."

Smith, a neurobiologist at Allegheny University of the Health Sciences, said there is a physical reason for PMS. She's studying a transmitter in the brain called GABA that helps a person to feel calm.

She discovered that because of changing hormone levels, GABA doesn't work very well in pre-premenstrual women. Since GABA's function is to make someone fell calm, if it's not working well, that person will feel anxious.

Smith also found that GABA doesn't function as well just after birth, which could help explain postpartum depression.

Currently, some doctors use anti-depressants or hormones to treat PMS. But these options don't always work well for everyone. Smith's work could lead to better treatments for the future.