What Is Abaloparatide?

1. How does abaloparatide build bone?

Two natural hormones act on the same receptor in bone and kidney, the PTH type 1 receptor (PTH1R). Parathyroid hormone (PTH) controls blood calcium. Parathyroid hormone-related protein (PTHrP) acts more locally, including in growing bone. Abaloparatide is a 34-amino-acid synthetic analog of PTHrP(1-34). According to the Tymlos label, it shares 76% of its sequence with human PTHrP(1-34) and 41% with PTH(1-34), the form used in teriparatide.

As with teriparatide, timing is everything. A short daily pulse stimulates osteoblasts, the cells that lay down bone, more than osteoclasts, which remove it. Constant exposure does the reverse. The teriparatide guide explains that principle in more detail.

Where abaloparatide differs is in how it binds. The receptor can sit in two high-affinity shapes, called R0 and RG. Hattersley and colleagues showed that abaloparatide binds more selectively to RG than PTH(1-34) does, which produces a shorter burst of cAMP signaling inside the cell. Since brief signaling favors bone formation and longer signaling favors calcium release from bone, the authors proposed this as a reason abaloparatide might build bone with less rise in calcium. That is a plausible mechanism from lab studies, not a proven explanation of the clinical results.

Other label details:

• Absolute bioavailability under the skin is 36%, and peak levels come about half an hour after an injection.
• Half-life is about 1 hour. It is broken into peptide fragments that the kidneys clear.
• Heart rate rises within 15 minutes of a dose and settles in about 6 hours.

2. What did the ACTIVE trial show?

ACTIVE, the Abaloparatide Comparator Trial In Vertebral Endpoints, was the pivotal study (Miller et al., 2016). It ran at 28 sites in 10 countries from 2011 to 2014 and enrolled 2,463 postmenopausal women, mean age 69, with low bone density and prior fractures, or very low density if over 65. They received blinded daily abaloparatide 80 mcg or placebo, or open-label teriparatide 20 mcg, for 18 months. In total, 1,901 completed the study.

The label reports the main results against placebo:

BMD means bone mineral density, measured by a DXA scan. Source: Tymlos prescribing information. The EMA summary for Eladynos gives a similar spine-fracture figure, 0.5% against 4.2%, in the 2,070 patients it analyzed.

What came after: ACTIVExtend

Gains from bone-forming drugs fade if nothing follows them. In ACTIVExtend, 1,139 women who finished ACTIVE on abaloparatide or placebo took weekly alendronate, a bisphosphonate, for up to 24 more months.

Bone density kept rising during the alendronate phase. Benefits were consistent across age, density and prior-fracture subgroups (Leder et al., 2019), including a small group of women aged 80 and over (Greenspan et al., 2020).

3. Does abaloparatide work in men?

The ATOM trial randomized 228 men aged 40 to 85 with osteoporosis two to one to abaloparatide 80 mcg or placebo for 12 months.

All differences were statistically significant. Fractures were not an outcome, which is why the US label frames the men’s indication as increasing bone density rather than reducing fractures. FDA approved that indication on December 19, 2022 (Drugs@FDA).

4. How does abaloparatide compare with teriparatide?

This is the question most people ask, and the answer is “similar, with some differences that favor abaloparatide on calcium and the hip.”

Sources: Tymlos label, ACTIVE and the teriparatide guide for Forteo’s label.

Evidence from head-to-head and real-world data

• Calcium. In ACTIVE, high blood calcium occurred in 3.4% on abaloparatide and 6.4% on open-label teriparatide (risk difference −2.96 percentage points, P = .006) (Miller et al.). This was a prespecified safety comparison.
• Hip density. ACTIVE also found significantly larger gains at the total hip and femoral neck with abaloparatide (Tabatabai et al., summarizing ACTIVE).
• Hip and nonvertebral fractures. A claims study by Tabatabai and colleagues matched 21,676 women aged 50 and over starting each drug. Over about 18 months, hip fractures occurred in 1.1% on abaloparatide and 1.4% on teriparatide (HR 0.83), and nonvertebral fractures in 4.4% and 5.0% (HR 0.88). Cardiovascular events were similar. Several authors were Radius employees or consultants, and observational studies cannot rule out differences between patients who got each drug.
• Pooled data. A 2025 network meta-analysis combining trials and real-world studies found an advantage for abaloparatide on nonvertebral fractures (OR 0.87) and hip fractures (OR 0.81).

A 2025 expert review by Fuggle and colleagues summed up the state of play: both drugs clearly work, ACTIVE suggested slightly greater efficacy for major fractures as an exploratory finding, and the potential differences need confirmation in properly designed studies. In ACTIVE, teriparatide was open-label and the trial was powered only for abaloparatide versus placebo.

5. Is abaloparatide approved, and how is it used?

Sources: Drugs@FDA, Radius Health, EMA, Tymlos label.

The US label covers postmenopausal women and men with osteoporosis at high risk for fracture, or who have failed or cannot tolerate other therapy. The labeled dose is 80 mcg under the skin of the abdomen around the belly button once a day, at about the same time, with calcium and vitamin D if diet falls short. The first few doses should be taken sitting or lying down. Before first use the pen is refrigerated; after first use it can stay at room temperature for up to 30 days. Each pen delivers 30 doses.

A skin-patch version was tested and did not match the injection. In a phase 3 trial of 511 women, spine density rose 7.14% with the patch against 10.86% with injections at 12 months, missing the noninferiority margin.

6. What are the side effects?

From the US label:

Antibodies to abaloparatide developed in 41% of women by 18 months, 26% of them neutralizing, without a detected effect on safety or efficacy.

7. What are the warnings?

• Severe allergic reactions. Added in August 2026: anaphylaxis, angioedema and hives have been reported. The drug is stopped permanently after a severe reaction.
• Osteosarcoma. Rats developed bone cancer in a dose-dependent way at 4 to 28 times human exposure; human relevance is unknown. FDA removed the boxed warning after “a thorough regulatory review of long-term post-marketing data in TYMLOS and the parathyroid hormone (PTH) class of drugs” (Radius). The label still says to avoid it with open growth plates, Paget’s disease, unexplained bone disorders, bone cancer or metastases, prior skeletal radiation or an inherited predisposition.
• Dizziness on standing. Orthostatic hypotension typically occurs within 4 hours of an injection.
• High calcium. Measured 4 hours after injection, high calcium occurred in 3% of women and men on abaloparatide. It is not recommended with primary hyperparathyroidism or other high-calcium disorders.
• Kidney stones. Urine calcium can be checked if stones are suspected.
• Pregnancy. It is not indicated for women who could become pregnant.

The EU product information is stricter. It lists pregnancy, breastfeeding, women of childbearing potential, high calcium, severely reduced kidney function and unexplained raised alkaline phosphatase as reasons not to use Eladynos, and asks doctors to assess heart risk first and monitor patients with heart disease (EMA). The 2025 network meta-analysis found no difference in cardiac events between abaloparatide and teriparatide and called the EMA’s extra caution possibly excessive (Beaudart et al.).

8. Do GLP-1 drugs cause bone loss?

The honest answer is “probably a little, in some people, and the data on the newest drugs are thin.” When body weight falls, some bone and muscle are lost along with fat (Anastasilakis et al., 2025). The question is whether GLP-1 drugs add anything beyond that, and whether it raises fracture risk.

A 2025 review by Anastasilakis and colleagues concluded that GLP-1 drugs have had neutral or mildly negative, not clinically significant, effects on bone markers and density in clinical studies, and that fracture risk does not appear to rise at clinical doses.

What is missing is a large, long trial of the high-dose obesity drugs with fractures as an outcome, in older adults who are already at risk. Several smaller bone studies are registered on ClinicalTrials.gov, such as a comparison of tirzepatide and liraglutide and a semaglutide bone health trial, but none we found includes abaloparatide.

9. Should abaloparatide be used during GLP-1 weight loss?

Not as a routine add-on. The approved use is osteoporosis at high fracture risk, judged on bone density, prior fractures, age and other risk factors. Losing weight on a GLP-1 drug does not, by itself, meet that bar. No study has tested whether starting abaloparatide during GLP-1 treatment changes bone density or fractures. The 2-year US lifetime limit is another reason not to use it without a clear indication.

What the evidence does support:

• Know your baseline. For people with risk factors for osteoporosis, a DXA scan before or early in treatment gives a reference point. DXA reports bone and lean mass from the same scan.
• Exercise matters. In Jensen’s trial, adding exercise to liraglutide kept hip and spine density in line with placebo.
• Calcium, vitamin D and protein. Eating much less can mean taking in less of these. Labels for both bone drugs assume adequate calcium and vitamin D.
• If osteoporosis is diagnosed, the choice between abaloparatide, teriparatide, antiresorptive drugs and others is the same as for anyone else, made with the prescriber who manages bone health.

There is no known pharmacological interaction between abaloparatide and GLP-1 drugs on the label. Both can cause nausea and dizziness, so starting them at the same time makes it harder to tell which is responsible. Abaloparatide does not build muscle; its trials measured bone only.

The GLP-2 hormone, a cousin of GLP-1 discussed on the teduglutide page, has also been shown to lower a bone breakdown marker in short studies, but no GLP-2 drug is approved for bone.

10. What can you track on abaloparatide?

The outcomes in the trials are the ones worth logging:

• Bone density. DXA results at spine and hip, with dates and, ideally, the same scanner each time.
• Fractures. Any new fracture, including spine fractures found on imaging.
• Dose log. Daily injection time and site, pen start date for the 30-day discard rule, missed doses, and a running total toward the 2-year limit.
• Symptoms. Dizziness or palpitations after a dose, nausea, headache and any allergic reaction.
• Labs. Blood and urine calcium with the time since the last injection.
• What comes next. The plan for the drug that follows abaloparatide, such as alendronate.

If you also take a GLP-1 drug, recording weight and body composition alongside these makes later DXA results easier to interpret. A peptide tracker or spreadsheet can hold that history; it cannot tell you whether your fracture risk has changed.

11. Abaloparatide FAQ

• What is abaloparatide used for?

  In the US, Tymlos is approved for postmenopausal women with osteoporosis at high risk for fracture, and to increase bone density in men with osteoporosis at high risk for fracture, including people who have failed or cannot tolerate other treatments. In the EU, Eladynos is approved for postmenopausal women only.

• What is the difference between abaloparatide and teriparatide?

  Both activate the same receptor, PTH1R, to build bone. Teriparatide is the first 34 amino acids of parathyroid hormone. Abaloparatide is based on parathyroid hormone-related protein and binds the receptor in a way that gives shorter signaling. In the ACTIVE trial it caused less high calcium and raised hip density more than teriparatide, but the trial was not designed to show that it prevents more fractures.

• What is the dose of Tymlos?

  The labeled dose is 80 mcg injected under the skin of the lower abdomen once daily, at about the same time each day. Each pen holds 30 doses and is discarded 30 days after first use. The first several doses should be given sitting or lying down because of the risk of dizziness on standing.

• How long can you take abaloparatide?

  The US label says safety and efficacy have not been evaluated beyond 2 years and that use for more than 2 years in a lifetime is not recommended. The EU product information caps treatment at 18 months. After stopping, an antiresorptive drug such as alendronate is usually used to keep the gains, as in the ACTIVExtend study.

• What are the side effects of abaloparatide?

  In women, high urine calcium, dizziness, nausea, headache and palpitations were more common than on placebo. Men reported injection site redness, dizziness and joint pain more often. The label warns about dizziness or fainting on standing, high blood calcium, kidney stones, severe allergic reactions and a bone cancer finding in rats.

• Can abaloparatide prevent bone loss on semaglutide or tirzepatide?

  There is no evidence on that. No published or registered trial we found tests abaloparatide in people taking GLP-1 drugs. It is approved for osteoporosis at high fracture risk, not for protecting bone during weight loss in general. Anyone concerned should ask about a DXA scan and fracture risk assessment.

• Does abaloparatide build muscle?

  No. It is called anabolic because it builds bone. Its trials measured bone density and fractures, not muscle mass or strength.

• Does abaloparatide cause cancer?

  Rats given high doses developed osteosarcoma, a bone cancer, in a dose-dependent way. Its relevance to people is unknown. FDA removed the boxed warning in December 2021 after reviewing long-term data on Tymlos and the PTH drug class, but the label still warns against use in people at higher baseline risk, such as those with Paget's disease or prior skeletal radiation.

12. Sources