Public Citizen issues warning against Forteo. (Cancer Implications Questioned).

An alert issued by the consumer watchdog group Public Citizen warns consumers to avoid using the osteoporosis drug teriparatide, because studies in rats have linked it to an increased risk of bone cancer.

But the drug's manufacturer, Eli Lilly, has countered that teriparatide (Forteo) has been used in more than 2,000 people in clinical trials, and not one case of osteosarcoma has been reported. And according to a Canadian bone mineral specialist interviewed for this article, bone growth in rats is fundamentally different from that in humans, so the animal data should not be extrapolated to patients who are using the drug.

Last month, the Washington-based Public Citizen issued a "do not use" alert for teriparatide, warning that the drug, which was approved by the Food and Drug Administration last November, may cause osteosarcoma.

"Teriparatide has led to bone cancer in laboratory animals, a risk that far outweighs the drug's benefit," the group wrote in a press release.

In its most recent monthly newsletter, "Worst Pills Best Pills," the group says it voiced its concerns to the FDA's Endocrinologic and Metabolic Drugs Advisory Committee in 2001.

"We testified that the ability of teriparatide to cause cancer--in this case osteosarcoma--in rats was some of the most striking animal carcinogenicity data we had ever seen. Tumors developed in the animals at even the lowest dose level of teriparatide administered, which was 1.6 times the dose intended for humans," according to the newsletter article.

"We would like to see individuals avoid this drug until there's evidence that it doesn't cause osteosarcoma," Public Citizen spokesperson Larry Sasich, Pharm.D., said in an interview.