Wrong Spoon Size Can Cause Medicine Mistakes
The dose seems smaller on larger-sized spoons, due to the size-contrast effect. (The shaded area is the dosing size, and the dotted line is the recommended dose of 1 teaspoon).
Credit: Jason Kosti / Cornell News Bureau.

When pouring out doses of cold medicine, you may want to ditch the kitchen spoon for a more exact measuring device, a new study suggests. Depending on the spoon’s size, people tend to pour too little or too much.

The study involved 195 university students who were asked to pour a teaspoon (5 mL) of liquid medicine into a medium-sized spoon and a large spoon. To give them a better understanding of the volume of a teaspoon, the researchers had students measure out the medicine first in an actual teaspoon before trying it out in the other two spoons.

Participants poured an average of 4.58 mL, or about 8 percent less than prescribed, into the medium spoon, and 5.58 mL, or nearly 12 percent more for the larger spoon. Even so, the students indicated above-average confidence that their pouring was accurate.

"Twelve percent more may not sound like a lot, but this goes on every four to eight hours, for up to four days," said lead researcher Brian Wansink, director of the Cornell Food and Brand Lab. "So it really adds up — to the point of ineffectiveness or even danger."

The participants were also in atypical conditions, pouring cold medicine in a well-lit room in the middle of the day. "But in the middle of night, when you're fatigued, feeling miserable or in a rush because a child is crying, the probability of error is undoubtedly much greater," he said.

Essentially, an optical illusion came into play called the size-contrast effect, in which we use one object as a reference point from which to measure a nearby object. For instance, an average-height guy standing next to an extremely tall friend would appear far shorter than if he stood next to a more petite man. 

"That's what's going on with pouring the medicine. One teaspoon into a three-ounce spoon looks like nothing, so you pour more," Wansink told LiveScience. That led to overdosing. The opposite effect plagued the medium-sized spoon.

About 70 percent of us grab silverware spoons to take liquid medicine, according to the Mayo Clinic. With the new study results, Wansink recommends instead that consumers use a measuring cap, dosing spoon, measuring dropper or a dosing syringe.

The study is detailed in the Jan. 5 issue of the journal Annals of Internal Medicine.