The weak dollar has greatly bolstered profits of US health care companies over the past year, but they could be hurt in coming months if the greenback continues to strengthen, Reuters writes.

Johnson & Johnson, which reported third-quarter earnings yesterday, predicted that fourth-quarter company sales will be crimped 1.5 percentage points by the resurgent dollar. That stands in contrast with J&J’s earlier prediction that a weak dollar would add 3.5 percentage points to sales in the period.

Mike Krensavage, principal of Krensavage Asset Management, says US drugmakers with the greatest percentage of overseas sales, such as Schering-Plough and Pfizer, would have the most to lose if the dollar keeps gaining value. That’s because a strong dollar lowers the value of overseas sales when they are converted back into dollars.

“Something that has been a tailwind is becoming a headwind for some companies,” Edward Jones analyst Linda Bannister tells the news service. Seamus Fernandez, an analyst with Leerink Swann, adds that the negative impact of the stronger dollar could be “substantial” to US drugmakers in the first through third quarters of 2009.

“Currency has been a great benefit to US drugmakers,” Krensavage tells Reuters, “but what the dollar giveth, the dollar can take away.”