Tymlos (abaloparatide) increases bone density by roughly 11% at the spine and 4% at the hip over 18 months of daily use. These gains are among the largest achievable with any current osteoporosis medication, and they translate into meaningful fracture protection during that same period.
Bone Density Gains at 18 Months
The pivotal clinical trial of Tymlos tested 80 micrograms injected daily under the skin in postmenopausal women with osteoporosis. At 18 months, bone mineral density increased at every measured site:
- Lumbar spine: +11.2% (compared to +0.6% with placebo)
- Total hip: +4.2% (compared to −0.1% with placebo)
- Femoral neck: +3.6% (compared to −0.4% with placebo)
All of these differences were statistically significant. The spine responds most dramatically because it contains a higher proportion of the spongy, metabolically active bone tissue that Tymlos targets. Hip gains are smaller in percentage terms but critically important, since hip fractures carry the highest rates of disability and death among osteoporotic fractures.
How Those Gains Reduce Fractures
Building bone density matters only if it prevents breaks, and the trial data here are encouraging. After 18 months, 3.3% of women taking Tymlos experienced a clinical fracture of any type, compared with 5.9% on placebo. For vertebral fractures specifically, the absolute risk dropped by 3.6 percentage points. In practical terms, treating 28 women for 18 months prevented one additional vertebral fracture that would have otherwise occurred.
How Tymlos Compares to Forteo
Forteo (teriparatide) is the other daily injectable bone-building drug, and the two work through a similar receptor on bone cells. In a head-to-head clinical trial called ACTIVE, Tymlos produced significantly greater bone density improvements at the total hip and femoral neck than Forteo. Spine gains were broadly similar between the two. The hip advantage is one reason some clinicians prefer Tymlos, particularly for patients whose hip density is a primary concern.
Why Tymlos Builds Bone Instead of Breaking It Down
Tymlos is a synthetic version of a naturally occurring protein fragment called parathyroid hormone-related peptide. It activates the same receptor that parathyroid hormone uses, but it does so in a slightly different way. The key distinction is duration of signaling. When that receptor is activated continuously, the body ramps up bone breakdown. When it’s activated in brief pulses, once a day, the signal instead stimulates the cells that build new bone. Because Tymlos binds the receptor in a configuration that produces a shorter burst of activity, it favors bone formation over resorption, even compared to Forteo.
How Treatment Works Day to Day
Tymlos is a once-daily injection of 80 micrograms, self-administered with a prefilled pen. You inject it into your lower abdomen, avoiding the two-inch area directly around your navel. The needle is small and the injection is subcutaneous, similar to what people with diabetes use for insulin. Most patients do it at the same time each day.
The maximum recommended treatment duration is two years over a patient’s lifetime. This limit exists because in rat studies, prolonged exposure at high doses caused bone tumors (osteosarcoma) at alarming rates. The FDA originally placed a boxed warning on the label for this reason, though it was removed in December 2021. Observational studies in humans have not shown an increased osteosarcoma risk, but data beyond two years of use remain limited. After completing Tymlos, patients typically transition to a different class of osteoporosis drug to maintain the bone they’ve built.
Common Side Effects
Because Tymlos affects calcium metabolism, some patients develop mildly elevated calcium levels. In clinical trials, 3% of women on Tymlos had elevated blood calcium measured four hours after injection, compared to 0.1% on placebo. About 11% experienced excess calcium in their urine (versus 9% on placebo), and 20% had an elevated urine calcium-to-creatinine ratio compared to 15% on placebo. For most people, these shifts are modest and don’t cause symptoms, but your provider will typically monitor calcium levels during treatment.
Men with osteoporosis showed similar rates of blood calcium elevation (3% versus 0% on placebo), though urine calcium levels were not significantly different from placebo in that group. Blood pressure increases have also been noted on the medication label as something to be aware of during treatment.
What Happens After You Stop
The bone density you gain on Tymlos doesn’t last on its own. Once you stop a bone-building drug, the new bone becomes vulnerable to the same resorption process that caused the original loss. This is why the standard approach is to follow Tymlos with an anti-resorptive medication, typically a bisphosphonate, which slows bone breakdown and locks in the density gains. Skipping this follow-up step can lead to rapid bone loss, particularly at the spine, within the first year after stopping.