For centuries, botulinum toxin has been known as the cause of the paralytic and sometimes fatal illness known as botulism. Best known by the brand name Botox, the toxin’s type A variant has a reputation as a cosmetic and is famous for smoothing furrowed brows.

Bahman Jabbari, M.D., professor of neurology, is among a small number of clinicians with expertise in the toxin’s many therapeutic uses. He and his Yale neurology colleagues are using it to treat a constellation of neurological disorders, migraine headaches and other complaints in a growing practice that saw 300 patients last year.

“It is a remarkable drug,” said Jabbari, the former chief of neurology at Walter Reed Army Medical Center in Washington, who was among the first researchers to establish the drug’s effectiveness in treating pain. “It is something that gives very few side effects, yet the patient sees results that are so dramatic, so sustained.”

Botulinum A is used to treat muscular symptoms in head trauma, stroke, cerebral palsy and multiple sclerosis. In these conditions, the relief comes from the toxin’s muscle-relaxing properties—the same properties that make it useful to combat wrinkles, said Jabbari. But, he added, the drug has a range of biochemical actions effective in many conditions, including excessive sweating and salivation. Botulinum A offers a palliative option in many cases where other medicines had been unable to offer much comfort.

“It is very satisfying to be able to give relief to patients with a chronic neurological disorder who previously had no hope,” said Jonathan M. Goldstein, M.D., associate professor of neurology and director of clinical services in the department.

Jabbari’s current investigations focus on pain relief, which he believes is the greatest area of potential for botulinum A. Patient H. Stuart Engar volunteered for one of Jabbari’s studies, hoping for a reprieve from excruciating neck pain. An undiagnosed neurological disorder had left Engar unable to work or perform such simple tasks as bending to unload the dishwasher. Though the study is completed, Engar continues to get botulinum A injections every three to four months for pain and mobility. He called the treatments “life-changing.”

On a recent visit, Jabbari administered a series of injections in carefully pinpointed muscles along Engar’s neck. In some cases, physicians use electromyographic guidance to make the injections. Jabbari asked Engar if he experienced side effects from the treatment. Like most patients, he did not. The most common side effects are flu-like symptoms and muscle weakness, the latter of which is often prevented by proper dosage, Jabbari said. There is no danger to patients who take botulinum A long-term, he added, because the toxin gets deactivated in the body after three months.

Patients do, nevertheless, express misgivings about Botox. When Huned S. Patwa, M.D., associate professor of neurology, picked up a syringe, the patient—a migraine sufferer—asked, “Do you know where it came from?”

She was referring to a Florida physician who injected patients with a counterfeit version of the drug. The unlicensed product contained much higher concentrations of the toxin, causing patients to contract botulism.

Ironically, botulinum’s promise as a weapon helped to unlock its healing potential. Army officer Edward J. Schantz, Ph.D., first purified botulinum toxin type A in a crystalline form in 1946 when the U.S. military was studying it as a weapon. Schantz later collaborated with Alan B. Scott, M.D., who used the toxin to relieve strabismus (crossed eyes) in monkeys. Over the course of 20 years they developed a version of the toxin that won FDA approval for testing on humans. They sold it to the pharmaceutical company Allergan, which branded the drug Botox. In 1989, the FDA approved it for the treatment of strabismus, blepharospasm and hemifacial spasm in patients over 12 years old.

Researchers like Jabbari see the drug’s future applications as broad and promising. For patients like Engar, clinical botulinum has already made a dramatic difference. “I can hold my grandchild,” he said. “That may seem like a small thing, but … no, that’s a big thing.”