Johnson & Johnson and Novartis AG’s Sandoz are voluntarily recalling a version of its blockbuster pain patch Duragesic after manufacturers said that certain defects may cause leaks that can lead to fatal overdoses.

The drug is prescribed for chronic pain in people used to narcotics, such as cancer patients.  Yet the Food and Drug Administration found cases where doctors prescribed if for headaches or post-surgical pain.

The recalled patches, manufactured by Alza Corp. and sold by PriCara and Sandoz Inc. in the U.S. and Canada, have expiration dates on or before December 2009. They may have an opening which could result in release of the gel made of the drug fentanyl inside. Exposure to fentanyl directly can cause serious harm, including breathing problems and overdose, which can be fatal, the New Brunswick, New Jersey-based company said in a statement, according to the Associated Press.

Fentanyl is an opioid analgesic with potency approximately eighty times that of morphine. Fentanyls have been also produced clandestinely and identified in the U.S. drug traffic. The biological effects of the fentanyls are similar to those of heroin, with the exception that many users report a noticeably less euphoric 'high' associated with the drug and stronger sedative and analgesic effects.

This is the fifth recall of some version of the patches since 1994.

“Perhaps the time has come for the FDA to order Johnson & Johnson to pull all versions of this product off the shelves,” said Alex MacDonald, a lawyer who represents the families of former patch users, according to Bloomberg.

Health experts urge people to flush down the toilet the damaged patches and not handle them. However, skin that has been exposed to the gel should be thoroughly rinsed with water, but not washed with soap.

Duragesic patches generated $1.16 billion in global sales last year, making them Johnson & Johnson’s eight-biggest selling product.