Research in the journal Food Quality and Preference sheds new insight into the role of pill color and shape in influencing patient perceptions on expected ease/difficulty of swallowing, taste, and/or efficacy – which may influence medication adherence and treatment compliance.

Perceived bitterness or metallic taste may contribute to poor medication adherence and compliance; while some drug manufacturers have encapsulated bitter-tasting compounds so they do not come into direct contact with the patient’s mouth, this is not feasible for all medications. In the study, researchers conducted two experiments to evaluate how cues from the color and shape of tablets could affect expected ease/difficulty of swallowing, taste, and/or possible efficacy of medications. In the first experiment, 97 participants from the United States viewed online photos of tablets having one of seven colors and three shapes (21 tablets total): circular-, oval-, and diamond-shaped tablets colored red, light-red, green, light-green, blue, light-blue, and unmodified as white. The participants ranked the tablets based on expected difficulty of swallowing, expected bitterness, expected alerting effect, and expected efficacy solely from visual elements of the tablets.

The participants reported that they expected the blue and light-blue tablets to taste less bitter than the other colors and red and light-red were expected to be more alerting compared to the other colors. White tablets were ranked as having an expected greater efficacy in treating symptoms of headaches. Diamond-shaped tablets were expected to be most difficult to swallow, whereas oval-shaped tablets were perceived to be the least bitter, the least effective in treating headache symptoms, and less alerting than the diamond-shapes tablets.

In the second experiment, 337 participants from China, Colombia, and the U.S. completed the same tasks but pink, yellow, and orange were also now included. Participants also had to also complete a color identification task at the end to ensure that they had accurately identified the correct color category.