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Tricks but no treats: Illusions and medication errors

From the October 30, 2002 issue

Various "tricks of the mind," including cognitive and visual illusions, affect accurate performance. Illusions are generally defined as systematic distortions between our thoughts, perceptions, and reality. Like a mirage in the desert, they lead us astray by creating incorrect assumptions about how to think, see, hear, or otherwise interpret events.

Physicians' prescribing patterns illustrate the problem of potential cognitive illusions well because their orders often are predictable. The doctor's name on an order for a common anti-infective, for example, may easily trigger automatic mental processes for what to dispense. If the physician usually orders 250 mg of the medication, a pharmacist or nurse may assume that 250 mg is required and miss cases in which the physician actually has ordered 500 mg. A misguided reliance upon memory of the physician's prescribing pattern produces this self-deception.

Visual and auditory illusions, on the other hand, arise from perceptual rules that misinterpret or fail to organize the information properly. Thus, we may see or hear things that are not actually present. Some medications, for example, are confused because their names and packaging have look-alike and sound-alike qualities (e.g., Serzone-Seroquel; Zyrtec-Zyprexa, Celebrex-Cerebyx). In this case, the names are blended visually or acoustically and one product is mentally transformed into the other. Such illusions resist correction, and thus persist throughout the medication use process, resulting in an error.

Are some illusions more likely to occur than others? A recent study examined how susceptible 51 pharmacists were to six situations that normally created misperceptions.1 Outcomes showed that pharmacists were more prone to: a.) misreading drug names or strengths on prescriptions and medication containers; b.) misjudging the spatial location of a product stored in a pharmacy; and c.) mistaking the size of a medication for a smaller look-alike counterpart. Participants were more successful in resisting problems with miscalculating quantity and miscopying prescription information.

While "tricks of the mind" do not affect everyone to the same degree (indeed, some people are able to resist their influence), interventions are needed for those that are most problematic. Outcomes of the study reinforce the need for barcode technology and electronic transmission of prescriptions to counter the misreading of drug names and strengths. While nurses and pharmacists still may be prone to spatial illusions that distort correct location when selecting products from storage areas, some errors can be averted by avoiding the practice of just "reaching and grabbing" the product when busy without careful examination that the correct product has been selected.

Finally, the study showed that size might not be a reliable cue to differentiate two medications that otherwise look alike or have names that are similar. Thus other ways to set items apart, including packaging, color, shape, and the use of auxiliary labels, may be needed. Rotating placement of fast moving medications also can help staff avoid the habit of "reaching and grabbing" for products based on their usual position on the shelf.

Reference: 1. Tranum D, Grasha A. Susceptibility to illusions and cognitive style: Implications for pharmacy dispensing. Perceptual and Motor Skills, 2002, In Press. For more information, contact Dr. Grasha at

ISMP thanks Anthony F. Grasha, PhD, Professor of Psychology, University of Cincinnati, for contributing this article.

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