Lemondrop

In addition to making you puffy and hostile, PMS has another awesome side effect: It causes you to blow your cash on extravagant purchases you can't actually afford.

A new study has established a link between female hormonal changes and shopping. The research, by psychologists from the University of Hertfordshire, found that women's spending fluctuates throughout the month and peaks around your very favorite time of the month.

Women tend to buy more than planned around the time of their menstrual cycles, with nearly 60 percent of those surveyed saying they'll spend around $40 more than necessary, while a further 6 percent admitted to dropping over $389 on luxury items like bags and shoes. (Naturally, because they were PMSing, they felt like crap about it afterward.)

The study also found that spending drops when women are at their most fertile. (Perhaps they tend to be otherwise occupied?)