Amgen and Wyeth have added the black box warning to the arthritis drug Enbrel after the drug has been linked to infections including tuberculosis. Enbrel is designed to work by soaking up an inflammatory protein called TNF. Enbrel had already had a bold warning placed on its prescribing label. The black box warning label will be the most serious warning issued by the FDA. Other arthritis drugs such as Vioxx have run into trouble in the last few years because of a link to heart attacks. Enbrel appears to have no such issue. However, the link to infections, especially tuberculosis warranted the black box warning label.