There’s something the tens of millions of Americans who are currently on GLP-1 medications, or thinking of starting them, need to know.

When patients rapidly lose weight, they also tend to lose muscle mass and bone density, which can increase their risk of fractures and long-term mobility issues. That’s why it’s so important for patients taking GLP-1s to work with their doctors — and pair the medicines with exercise and strength training.

GLP-1s work by mimicking glucagon-like peptide-1, a hormone in the body that regulates blood sugar, appetite, and digestion. Essentially, the drugs make patients feel full longer, which reduces food intake and predictably leads to weight loss. Patients can lose 5%-20% or more of their body weight within a year of therapy, and also see significant improvements in their cardiovascular health.

But when people shed those pounds, they also tend to lose muscle and bone. About 25% of the total weight loss tends to come from a decline in musculoskeletal mass.

That, in turn, may increase the risk of fractures, especially in older adults. While data on fractures among individuals using GLP-1s is still limited, one study found that older adults with type 2 diabetes using GLP-1s had an 11% increased risk of fractures.

Older women and those in perimenopause may be particularly vulnerable. Women already lose muscle mass and bone density as their estrogen levels fall during menopause — they can lose 10-20% of their peak bone mineral density during the menopause transition. Concomitant GLP-1 use can exacerbate those losses.

This evidence does not mean that older patients cannot use or benefit from these medications; however, they do need to be aware of these secondary effects — and work with their doctors to mitigate them.

Initially, patients should have a thorough conversation with their physicians about the benefits and risks of GLP-1s — especially if patients are broadly healthy and are interested in the drugs for mostly cosmetic reasons.

Patients should also consult their doctors to develop a treatment plan that prioritizes exercise and strength training. That combination treatment — GLP-1s paired with exercise — can simultaneously promote weight loss while preserving bone and muscle health. Strength training, in particular, helps stimulate bone growth and may boost bone mineral density.

Patients should also ensure proper nutrition, following diets high in protein, calcium, vitamin D, and magnesium to promote muscle and bone health.

At times, GLP-1s can seem like miracle drugs. Though they were originally developed to help patients combat diabetes and lose weight, emerging research suggests they also improve cardiovascular health and may have potential beneficial effects on kidney disorders, osteoarthritis, and even addiction.

Given how powerful they are, it’s easy to see why 12% of Americans have already taken one, and why that share is increasing by the day.

But losing weight is supposed to improve our health, not put it at risk. Patients need to familiarize themselves with the drawbacks, not just the benefits, of these medicines — and collaborate with their doctors to safeguard their long-term muscle strength and bone health as much as possible, rather than purely shrinking their waistlines.

The opinions expressed in Fortune.com commentary pieces are solely the views of their authors and do not necessarily reflect the opinions and beliefs of Fortune.

breaks the traditional barrier between audience and newsroom. The show transforms

Fortune DailyFortune’s trusted reporting into actionable, conversational, and entertaining insights for an emerging class of business leaders.

Watch here.