Patients taking Plavix will now be able to read a warning written on the drug. This would be specifically for those who have a poor response to the drug. US regulators said that due to patients not responding to the drug are unable to break down the drug well.

The $8-billion-a-year drug sold by Bristol-Myers Squibb Co and Sanofi-Aventis SA, will carry the boxed warning, the Food and Drug Administration said.

FDA's website states that patients who are poor metabolizers of Plavix will be warned about its effectiveness.

Reports say that people who are poor metabolizers have bodies that do not effectively convert Plavix to its active form.

Mary Ross Southworth of the FDA's Center for Drug Evaluation and Research said, "Because the patient makes less of the active form there is less anti-platelet effect in the blood and the patient may not receive the full benefit of Plavix treatment."

FDA informed that about two to 14 per cent people are poor metabolizers of Plavix.

This warning would enable doctors to identify people who are unable to break down the drug.

Plavix loses patent protection in 2012 and is the second-best selling drug in the world.