March 31, 2023, 5:49 PM EDT By Erika Edwards and Kristen Dahlgren NBC News

Is it ‘voodoo’ or does a procedure called a stellate ganglion block help patients with long Covid-related loss of smell or taste?

An experimental procedure that involves injecting an anesthetic into a bundle of nerves in the neck is being studied as a possible way to restore lost sense of smell in people with long Covid.Justine Goode / NBC News / Getty Images

A numbing procedure usually used to treat pain and post-traumatic stress disorder is being tested as a way to restore smell and taste in people with long Covid.

It’s called a stellate ganglion block. In the procedure, a doctor uses a temporary, local anesthetic — like what a dentist would give before filling a cavity — and injects it into a specific bundle of nerves called the stellate ganglion on both sides of a person’s neck. The nerves are part of the sympathetic nervous system, which controls automatic bodily functions, such as blood pressure, digestion and heart rate.

The area is not known to have any impact on how a person perceives odors, however, leaving some experts skeptical of the approach. Other doctors say they have seen real improvements in patients who either can’t smell anything or find previously delicious food and drinks now taste repulsive.

Long-Covid patients find hope in treatment aiming to restore taste and smell

Smell disorders tend to become more common with age, and affect millions of people. As many as 1 out of every 8 people in America over age 40 have some kind of olfactory dysfunction, according to the National Institute on Deafness and Other Communication Disorders.

A survey last year found that about 15% of people with Covid-related olfactory loss still had trouble smelling correctly six months later.

Not many treatments are available for smell disorders. Doctors may try olfactory retraining, in which patients concentrate on sniffing four scents — usually rose, eucalyptus, lemon and clove — twice a day for at least three months. Smell therapy has shown promise in some clinical trials.

Getting smell back

At Cleveland Clinic, doctors are offering stellate ganglion blocks to long Covid patients, with the hope of launching a clinical trial.

Jennifer Henderson, 54, of Franklin, Ohio, got Covid in January 2021 and immediately lost the ability to taste or smell anything. A year later, her senses came back, but were wildly distorted.

She first tried olfactory retraining “religiously” for months, without success. Peanut butter and ranch dressing still smelled like chemicals.

Chicken was the worst, she said. “It tasted like rotting flesh. I had to spit it out.”

Finally, in November last year, she received the stellate ganglion block at the Cleveland Clinic. The effect was immediate. She held a fresh cup of coffee up to her nose and burst into tears.

“It was the best smell ever,” Henderson said. “I just cried like a baby.”

Watch: Patient regains ability to smell after experimental procedure

Dr. Christina Shin, a physician specializing in pain management at the Cleveland Clinic, said that nearly every day at least one or two patients are referred to her from the long Covid clinic affiliated with the hospital system for help with their smell and taste.

She has treated roughly 30 long Covid patients with the block. About half get better, she estimates, though the level of improvement varies between 25% and 90%.

Dramatic responses like Henderson’s have made the rounds on social media, igniting enthusiasm in long Covid communities. But many doctors are cautious because no one really understands how it works.

Some experts theorize that it may increase blood flow to the brain. Others suggest the block acts as a “reset button” for the sympathetic nervous system.

Some question whether it works at all.

“There is no scientific evidence that this is effective,” said Dr. Justin Turner, an associate professor in the department of otolaryngology–head and neck surgery at Vanderbilt University Medical Center in Nashville, Tennessee.

“Given the lack of data suggesting efficacy, it’s really hard to advocate for this for patients who have a problem that typically resolves with time,” he said.

As many as 80% will recover on their own within about six months, said Dr. Zara Patel, a professor of otolaryngology at Stanford University.

That’s because stem cells in the nasal cavity have the ability to turn into brand new olfactory receptor neurons that detect odors.

“Throughout our lifetime, probably every three to four months, each olfactory receptor neuron dies off, and a new olfactory receptor neuron comes in and takes its place,” Patel said.

Sometimes those new neurons get confused after they regenerate, leading chicken to smell like rotten flesh, as in Henderson’s case.

Distorted smell, called parosmia, isn’t just about difficulty during mealtimes. The condition can have a profound and deeply upsetting impact on a person’s life.

In 2021, researchers in the United Kingdom surveyed people with Covid-related parosmia. Some worried about the effect it had on how they felt about their children.

“A lot of my maternal bonding feelings for my children are tied up with smell,” one woman said in the study.

More news on smell disorders

• Phantom smells may be a sign of trouble.
• Smell disorders, such as detecting burning hair, may be more common than thought.
• Loss of smell may be a warning sign of Alzheimer’s disease.

Some reported that the problem was ruining their sex lives. One person wrote about a partner’s “rotten breath.” The stench was “unbearable, no matter how hard I tried to put it out of my mind.”

Some patients fall into despair.

“I have had many patients crying in my office telling me that the parosmia — not just the smell loss, but the smell change — is destroying their life,” said Dr. Nyssa Farrell, an assistant professor of otolaryngology-head & neck surgery at Washington University School of Medicine in St. Louis.

However, she was wary of anecdotes of people getting better after a stellate ganglion block.