The Food and Drug Administration has ordered the makers of Darvocet and similar drugs containing propoxyphene to carry a stronger warning about the risk of potential overdose. The agency declined to pull the drug from the market despite calls from consumer groups to do so. Propoxyphene-containing drugs have been linked to nearly 100 deaths in the last 40 years. However, experts believe that number represents only a fraction of total fatalities caused by propoxyphene.