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Wednesday 23rd May 2018

Caution: coloured medication and the colour blind

7th September 2009

Colour is a good way to differentiate tablets and their containers because it enables more immediate recognition than do words printed on labels or embossed onto tablets.


Moreover, patients with poor vision or those not wearing their reading glasses can have difficulty reading print on labels or tiny low-contrast embossed text on tablets.

However, 8% of men and 0·4% of women have impaired colour-vision, of whom half are unable to recognise the main colours used in colour coding1. In a survey of 100 people with impaired colour-vision, 2% reported that they had confused their medication because they had mistaken the colour of tablets 2.

The appearance of warfarin tablets and containers to individuals with moderate or severe red–green deficiencies of colour vision are shown in the figure. The pink tablet appears blue and the green tablet appears grey.

Doctors and pharmacists should only use colour to instruct patients on how to identify tablets if they know that the patient has normal colour vision. People with red–green colour deficiency can recognise yellow, blue, grey, and white1- perhaps manufacturers should incorporate this information into guidelines about the use of colour for tablet identification.

1 Cole BL, Lian KY, Sharpe K, Lakkis C. Categorical colour naming by persons with abnormal colour vision. Optom Vis Sci 2006; 83: 879–86.
2 Steward SM, Cole BL. What do colour vision defectives say about everyday tasks? Optom Vis Sci 1989; 66: 288–95.


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