Patients who came down with botulism poisoning after being injected in the face with an unlicensed cosmetic product received up to 40 times the estimated lethal dose for humans, a new study says.

The four patients were hospitalized in November 2004. Fortunately, they were given enough anti-toxin to save their lives. Botulism is a rare paralytic illness caused by the toxins of the spore-forming bacterium Clostridium botulinum. Because it can cause such serious problems as slurred speech, difficulty swallowing and paralysis, it must be treated early. In severe cases, the paralysis can restrict breathing, requiring a ventilator.

Medicinal uses of weakened forms of the toxin include smoothing facial wrinkles.

A nearly two-year investigation by researchers at the U.S. Centers for Disease Control found the effects of the injections received by the four patients were long lasting, with one patient staying on a mechanical ventilator for 171 days.

All four are still feeling the effects today, Dr. Daniel Chertow of the CDC in Atlanta and his colleagues report in Wednesday's issue of the JAMA (Journal of the American Medical Association).

The patients were given botulism toxin A that was clearly labelled for research purposes only.

Use only licensed products: authors

"Physicians and patients must be aware of the hazards associated with illegitimate use of unlicensed botulinum toxin products. Only licensed products should be used clinically," the study's authors wrote.

"Entities inappropriately marketing, selling, or using unlicensed botulinum toxin products should be sought and subjected to full criminal and civil penalties."

A doctor in Florida was sentenced to three years in jail for using an unapproved drug in relation to the cases of the four patients.

A 100-microgram vial of the toxin that was given to the patients had enough botulism in it to kill more than 14,000 people.