Losing weight is good for the spine. However, physicians say rapid weight loss can lead to issues with bone quality, particularly in older adults.

Doctors say that some patients who are taking GLP-1 drugs to lose weight have reported that their back pain has improved.

Some of the millions of Americans taking a GLP-1 drug to lose weight are getting an unexpected benefit: Their back and knee pain is getting better.

Doctors who specialize in back and knee pain say that some patients are showing up in their clinics with anecdotes about less pain and better mobility after losing weight while taking medications like Novo Nordisk's (DK:NOVO.B) (NVO) Wegovy or Eli Lilly's (LLY) Zepbound.

"If you reduce obesity or reduce your weight, that decreases the load that your spine has to carry or the load that your knees have to carry every time you take a step, every time you go up and down stairs," said Geet Paul, director of interventional pain medicine at George Washington University Hospital. "That decrease in the weight definitely slows down progression of degeneration in the spine or in the joint."

But the clinical evidence so far is mixed. A few small studies have demonstrated that pain is reduced, while others have not. Doctors also say that certain patients, usually older adults, postmenopausal women or people who have never exercised, are suddenly dealing with back or bone issues after experiencing rapid weight loss. This is likely due to the loss of muscle or to a diet lacking in protein and other nutrients.

"The single most important issue that I see, however, are older folks who get on GLP-1s," said Nolan Fisher, a neck and back pain specialist at the Banner Health hospital system in Phoenix. "They lose a rapid amount of weight, and it actually deteriorates their bone quality."

That GLP-s can either relieve back and knee pain or bring on musculoskeletal issues due to rapid weight loss is indicative of how little we know about how these powerful medications work. These drugs can change patients' lives in beneficial ways, but there are still risks to be aware of, particularly when it comes to knee and back health in older adults.

"We're going to find out that GLP-1s help back pain," said Andrew Bach, a physiatrist at the Cedars-Sinai Spine Center in Los Angeles, "and I wouldn't be surprised if we find out that they also cause back pain in some people."

Back pain is complicated

The science isn't clear about why or even if GLP-1 drugs may alleviate back or knee pain.

Losing weight, whether through diet and exercise or taking a GLP-1 medication, reduces the pressure on spinal discs and vertebrae and the hinge of the knee. Once that happens, people's behavior often changes, because they feel a "rush of motivation" that commonly follows losing weight, according to Paul. They may be more open to going to the gym or physical therapy or doing at-home stretches - all proven ways to address back and knee pain. Some doctors also expect that these drugs have an anti-inflammatory benefit that could help these patients, particularly those with knee pain.

"You remove weight, but you also knock down inflammation," said Tim Church, chief medical officer at Wondr Health, a company that works with patients with chronic conditions to help them change their behavior. "And that translates into greatly reduced pain scales."

Drugs like Wegovy and Zepbound are increasingly used for a wide range of ailments. Not only do they treat Type 2 diabetes and help people lose weight, they are approved to help reduce related issues like heart attacks or to treat sleep apnea. If there is a proven reduction in pain, that's a big deal for Americans dealing with back and knee pain.

"People don't care about their LDL cholesterol. People don't care about triglycerides," Church said. "People care if they're in pain. People care if they can't play with their grandkids. People care if they can't walk up the stairs to see the Chicago Bears."

That makes sense. Chronic low back pain is a debilitating and costly medical issue that affects 13% of Americans. Patients often end up being treated by more than one doctor and have to try out a mix of treatments, which can be as simple as taking ibuprofen or as complex as surgery.

There are numerous studies looking at which medical interventions could help patients with low back pain. Therapy, yoga and acupuncture can alleviate pain. So can walking - as determined by one study that compared people who walked more than 100 minutes a day with those who walked less than 78 minutes a day. Most of the time, surgery doesn't help.

In a study published in August, a group of U.S. doctors reviewed the available research and concluded that GLP-1 drugs should be part of the treatment strategy for patients who are overweight or obese and dealing with chronic pain, particularly knee and joint osteoarthritis. The medications "are not analgesics in the traditional sense, but they are becoming increasingly relevant to pain medicine," they wrote.

The high-dose version of Wegovy is the only GLP-1 drug that's approved to treat pain of any kind - in Europe, the label cites data from a randomized, placebo-controlled trial showing Wegovy can reduce the pain associated with knee osteoarthritis. A company spokesperson said Novo isn't planning to seek a similar approval in the U.S. However, it is testing zenagamtide, a promising new weight-loss drug, in Phase 3 studies as a possible treatment for knee osteoarthritis, according to corporate filings.

Lilly is taking a similar approach. It's testing eloralintide and its GLP-1 pill Foundayo to see if either can lessen osteoarthritis pain. The company is also running a Phase 3 trial for retatrutide, a highly anticipated weight-loss drug that's in development, as a treatment for chronic low back pain.

"I'd say that [knee osteoarthritis] has the most research out there where weight loss can affect the pain," said Ryan Hoke, a physiatrist at the Pacific Medical Centers Specialty Care clinic in Bothell, Wash. "Obesity is a big risk factor for pain and symptomatic progression of knee osteoarthritis."

Doctors say older adults face the biggest musculoskeletal risks related to rapid weight loss, an important consideration given that GLP-1 medications for weight loss are now covered by Medicare.

One concern is the risk of a compression fracture, which is when a vertebra collapses, usually as a result of osteoporosis, according to Banner Health's Fisher. Osteoporosis is a bone disease that mostly affects older women and raises the risk that a fall could cause a break in the hip, spine or other bones.

"I've had several patients now, probably at least a solid five to 10 patients, who have dropped significant weight on the GLP-1s," he said. "Their osteoporosis has worsened, and they've ended up suffering compression fractures in their back as a result of the decreased density of their bones."

Even so, doctors say that adults with back or knee pain who are in their 30s, 40s or 50s, especially those who are active, usually benefit from weight loss, whether that's done their own or with the help of a GLP-1 medication. But it's not a sure fix - and understanding the risks matters.

"Back pain is multifactorial," Paul said. "When we're losing weight, we want to also be careful not to lose muscle mass as well, because that could be detrimental."

-Jaimy Lee