PMS 101

What Causes PMS?

Scientists don't know exactly why women get PMS or why some women experience it more severely than others. But they believe that it stems from a combination of hormonal changes, genetics, nutrition and psychological factors.

The Menstrual Cycle

Hormones are one of the most studied aspects of PMS's origins. PMS occurs near the end of a woman's menstrual cycle, within seven to 14 days before menstruation. During this cycle, which takes about 28 days, an egg matures and is released from the ovaries for possible fertilization. The hormones estrogen and progesterone play a big part in the menstrual cycle.

At around five days into the menstrual cycle, the ovaries release the female hormone estrogen. This hormone helps thicken the uterus, which will nourish an embryo if conception occurs. At around 14 days into the cycle, the egg is released in a process called ovulation. After ovulation, the last (luteal) phase of the menstrual cycle begins, and PMS symptoms tend to emerge. During this phase, the ovaries increase production of estrogen and begin producing progesterone to prepare the uterus for a possible pregnancy. If the egg is not fertilized, production of estrogen and progesterone drops. This hormonal drop causes the lining of the uterus to die and slough off, leading to menstruation. Once menstruation starts, PMS symptoms stop with a day or two. (See How Menstruation Works to learn more about the menstrual cycle.)

Researchers believe that the hormones estrogen and progesterone interact with certain brain chemicals, called neurotransmitters, and that this interaction can affect mood and contribute to other PMS symptoms. Let's take a look at some of the specific neurotransmitters researchers believe are involved in PMS.

Hormones and Neurotransmitters

Researchers believe that the following neurotransmitters are affected by estrogen and/or progesterone during the menstrual cycle and may lead to some of the symptoms of PMS:

  • Serotonin regulates mood and sleep patterns and creates feelings of well-being. Reduced levels of estrogen during the luteal phase may be linked to a drop in serotonin. Lower serotonin levels are associated with depression, irritability, anger and carbohydrate cravings, all of which are symptoms of PMS.
  • Gamma-aminobutyric acid (GABA) is a neurotransmitter associated with anxiety and depression. Progesterone may increase the activity of this neurotransmitter.
  • Endorphins increase feelings of pleasure and reduce the intensity of pain. Both estrogen and progesterone may affect endorphin levels.
  • Norepinephrine and epinephrine are neurotransmitters involved in the body's stress response. Estrogen may affect the levels of these neurotransmitters, which can influence blood pressure and heart rate as well as mood.

Whether symptoms are influenced by increased or decreased levels of estrogen and progesterone is a matter of some debate. Studies routinely produce conflicting results. Some researchers believe that the key to PMS symptoms lies in the balance between these two hormones during the menstrual cycle.