When you're taking or giving liquid medicines, measuring with ordinary kitchen spoons increases the risk of dangerous dosing mistakes, says a new study published in the Annals of Internal Medicine.

Former cold and flu sufferers were asked to pour one teaspoon of nighttime flu medicine into kitchen spoons of differing sizes. Depending upon the size of the spoon, the 195 former patients poured an average of 8 percent too little or 12 percent too much medicine.

"When pouring into a medium-size tablespoon, participants under-dosed. But when using a larger spoon, they poured too much medicine," study leader Dr. Brian Wansink, Director of the Cornell Food and Brand Lab, said in a statement.

"Twelve percent more may not sound like a lot, but this goes on every four to eight hours, for up to four days," Wansink explained. "So it really adds up—to the point of ineffectiveness or even danger."

Visual illusions and spatial relationships are familiar topics in Wansink's work in food and eating behavior. In his book Mindless Eating: Why We Eat More Than We Think, he shows how smaller plates can unknowingly decrease how much people eat, and how taller glasses can decrease the amount of alcohol poured by even expert bartenders.

"Simply put, we cannot always trust our ability to estimate amounts," said the study's co-author, Dr. Koert van Ittersum, Assistant Professor of Marketing at Georgia Tech. "In some cases it may not be important, but when it comes to the health of you or your child, it is vital to make an accurate measurement."

Wansink and van Ittersum recommend using a proper device, such as a measuring cap, dropper, or dosing spoon to measure liquid medicine.