Sweden also has a high self-reported rate of postcoital pill use.

Some research shows that the length of pill use can affect the chances of having a cardiovascular complication.

Each successive year of pill use seems to reduce the risk of this cancer by about 8 percent.

"There is a gap of about a decade between what the label says and the realities of pill use."

In its study, the cancer institute will focus on pill use and breast cancer in women under the age of 45.

It seems unlikely, therefore, that the ability to adjust for body weight would have materially affected the results that relate to pill use.

"We cannot yet know, or even imagine, what some of the additional serious consequences of extended pill use will be," she said.

After adjusting statistically for the difference between the sample sizes, the jump in sleeping pill use was 85 percent, the company said.

Then the Centers for Disease Control published its large study showing no association between pill use and breast cancer.

Fertility still remains low, despite lower pill use.