Tymlos (Abaloparatide) in Adolescents Ages 12 to 17: What We Know About Off-Label Use

What Is Abaloparatide and Why Would a Teenager Use It?

Abaloparatide is a synthetic analog of parathyroid hormone-related protein (PTHrP), approved by the FDA in April 2017 for postmenopausal women with osteoporosis at high fracture risk, and later for adult men. It works by selectively activating the PTH1 receptor in a way that favors bone formation over resorption. The key ACTIVE trial showed an 86% reduction in new vertebral fractures versus placebo over 18 months in postmenopausal women, establishing its clinical role in adults.

In adolescents, the reasoning for off-label use is narrow but real. Some teenagers, particularly girls with chronic illness, long-term glucocorticoid exposure, anorexia nervosa, or rare genetic bone disorders, develop severe secondary osteoporosis with fractures that do not respond adequately to first-line treatments like bisphosphonates or denosumab. In those situations, a bone-forming agent is theoretically appealing because you are trying to build bone, not just slow its loss.

The problem is that abaloparatide has never been tested in a completed, published Phase 3 trial in adolescents. What exists is sparse: case reports, small open-label series, and extrapolated adult pharmacokinetics. That gap matters enormously, and any clinician or parent researching this drug for a teenager deserves a clear-eyed look at exactly what is and is not known.

How Adolescent Bone Physiology Differs From Adult Bone

Bone is not static. Between ages 12 and 17, the skeleton is in one of its highest-velocity remodeling phases, second only to infancy. Approximately 40 to 60 percent of peak bone mass is laid down during adolescence, with peak accrual velocity occurring around ages 12 to 13 in girls. Girls typically reach approximately 90 percent of their peak bone mineral density by age 18.

Sex hormones drive this process. Estrogen from the ovaries triggers closure of the epiphyseal growth plates and coordinates with IGF-1 to deposit cortical and trabecular bone. Disruption of this process, whether from hypothalamic amenorrhea, premature ovarian insufficiency, or chronic disease, can permanently reduce peak bone mass, raising fracture risk decades later.

PTH and PTHrP receptors (the targets of abaloparatide) are active during skeletal development. Animal studies in growing rodents showed that high-dose PTH analogs accelerated osteosarcoma formation in rats with open epiphyses. Whether this translates to human adolescents is unknown, but it is the biological foundation for the boxed warning and the regulatory caution.

Which Adolescent Girls Are Sometimes Considered for Abaloparatide?

Clinicians at academic medical centers occasionally consider abaloparatide off-label for adolescent females who meet all of the following informal criteria:

• Documented severe osteoporosis (Z-score below negative 2.5 on DXA with fragility fractures, using age- and sex-matched norms)
• Failure of or contraindication to first-line anabolic or antiresorptive therapy
• Closed or nearly closed epiphyses confirmed on plain radiograph
• No personal or family history of primary bone malignancy or prior radiation to the skeleton

Even then, use is exceptional rather than standard. The International Society for Clinical Densitometry (ISCD) uses Z-scores rather than T-scores in anyone under 50, and specifically cautions against applying adult osteoporosis thresholds to children without fracture context.

The Evidence (and Its Limits) in Ages 12 to 17

The honest answer is that the published evidence base for abaloparatide in adolescents is thin. Very thin. Here is a structured look at what exists.

What Animal and Preclinical Data Suggest

The osteosarcoma signal comes from Fischer 344 rats given lifelong high-dose PTH analog exposure from weaning. The relevance to a human teenager receiving a time-limited course (typically 18 to 24 months) is debated, but the FDA has not lifted the boxed warning for any patient group, including adolescents. In growing animals, abaloparatide did increase periosteal bone formation and trabecular bone volume, which is the mechanistic rationale for its theoretical appeal in adolescents with deficit bone mass.

Human Data: What Actually Exists

As of early 2025, there is no published randomized controlled trial of abaloparatide in patients under 18. A small number of case series, primarily from European centers treating pediatric osteogenesis imperfecta (OI) or glucocorticoid-induced osteoporosis, have described off-label PTH analog use, but most of these used teriparatide (PTH 1-34) rather than abaloparatide. Direct abaloparatide data in adolescents is essentially limited to individual case reports and pharmacokinetic modeling.

The WomanRx clinical framework for evaluating off-label bone therapy in adolescent females uses three checkpoints: (1) confirmed skeletal maturity by growth plate imaging before initiating any PTH analog; (2) documented failure of at least one guideline-supported therapy at adequate dose and duration; and (3) shared decision-making that explicitly covers the osteosarcoma warning, the absence of pediatric trial data, and the need for reliable contraception throughout treatment and for 4 weeks after the last dose.

What We Can Extrapolate From Adult Women's Data (With Caution)

The ACTIVE trial enrolled 2,463 postmenopausal women with a mean age of 69, a mean lumbar spine T-score of negative 2.9, and a baseline vertebral fracture prevalence of 24 percent. Lumbar spine BMD increased by 9.2 percent from baseline at 18 months. Total hip BMD increased by 3.6 percent. These numbers reflect adult postmenopausal physiology, low baseline turnover, and estrogen deficiency, a completely different hormonal environment from a 15-year-old girl.

Pharmacokinetic extrapolation from adults to adolescents is not straightforward. Body weight, renal clearance, volume of distribution, and receptor density all differ. Without pediatric PK studies, dosing in teenagers remains entirely empirical.

Sex-Specific Physiology: How Being Female Shapes This Decision

Girls have a shorter and earlier window of peak bone accrual than boys. The consequences of severe osteoporosis in adolescence extend across the entire lifespan: a 16-year-old girl who sustains vertebral fractures is looking at 60 or more years of skeletal vulnerability. That urgency is real. At the same time, female-specific factors introduce complexity that adult trial data does not address.

Menstrual Status and Bone Health

A girl's menstrual status is one of the most important clinical variables when assessing bone health. Functional hypothalamic amenorrhea, common in athletes and girls with restrictive eating, causes estrogen deficiency that drives bone loss at the same biological mechanism as menopause, but at a developmental moment when bone is supposed to be accumulating. The 2017 Endocrine Society Clinical Practice Guideline on functional hypothalamic amenorrhea notes that bone loss can be substantial and that estrogen replacement, not PTH analogs, is the recommended first step for bone protection in this context.

If an adolescent girl has active amenorrhea from any cause, the baseline hormonal deficiency must be addressed alongside any anabolic drug therapy. Adding abaloparatide without correcting estrogen status is unlikely to produce optimal bone response, and there are no data to suggest it would.

Hormonal Contraception and Bone Mass

Many adolescent girls considering or using abaloparatide will also be on or need hormonal contraception. Depot medroxyprogesterone acetate (DMPA) is associated with bone density loss in adolescents, and combining it with an experimental bone therapy would require careful monitoring. Combined estrogen-progestin contraceptives are generally neutral to mildly beneficial for bone. Any adolescent on abaloparatide off-label should be using a reliable contraceptive method, and the choice of that method should itself be bone-considered.

PCOS and Secondary Bone Effects

Girls with polycystic ovary syndrome (PCOS) who have irregular cycles and chronic anovulation may have suboptimal estrogen exposure during peak bone accrual. PCOS is common, affecting approximately 8 to 13 percent of reproductive-age women. If a teenager with PCOS also has a secondary cause of bone loss (such as long-term glucocorticoid use for a comorbid autoimmune condition), she could theoretically be among the rare candidates considered for aggressive bone therapy. The evidence base for abaloparatide specifically in PCOS-related bone disease is absent.

Pregnancy and Lactation: A Required and Urgent Discussion

This section is not optional for any drug article on WomanRx, and it is especially important for a drug being considered in sexually active adolescents.

Pregnancy

Abaloparatide is contraindicated in pregnancy. Animal reproductive studies showed fetal harm at doses producing exposures comparable to human therapeutic levels. There are no adequate human pregnancy data. The drug is classified under the newer FDA Pregnancy and Lactation Labeling Rule (PLLR) with labeling that states it should not be used in pregnancy.

Any adolescent female prescribed abaloparatide off-label must be using a highly effective non-DMPA contraceptive method before starting therapy, throughout treatment (the approved course is up to 18 months; some off-label protocols extend to 24 months), and for at least 4 weeks after the final injection. This is not a negotiable clinical point. It must be part of the informed consent conversation.

If an adolescent becomes pregnant while on abaloparatide, the drug should be stopped immediately and the patient referred for obstetric care with full disclosure of the exposure.

Lactation

Whether abaloparatide transfers into human breast milk is unknown. The prescribing information states there are no data on the presence of abaloparatide in human milk, its effects on the breastfed infant, or its effects on milk production. Given this absence of data and the theoretical risk of fetal and infant harm from PTH analog exposure, use during breastfeeding is not recommended. For the rare postpartum teenager being considered for this therapy, breastfeeding should be discussed as a contraindication in the current evidence context.

Who This Is Right For (and Who It Is Not)

No treatment decision exists in a vacuum. Here is a direct breakdown by life stage and clinical profile.

This May Be an Option For:

• An adolescent girl aged approximately 15 to 17 with radiographically confirmed closed epiphyses, severe secondary osteoporosis with multiple fragility fractures, and documented failure of bisphosphonate therapy at appropriate doses for at least 12 months
• A teenager with osteogenesis imperfecta type I or III after a multidisciplinary bone team evaluation at a center with pediatric metabolic bone expertise
• A girl with glucocorticoid-induced osteoporosis on ongoing immunosuppressive therapy where bisphosphonates are contraindicated or have failed, and where teriparatide has been considered and rejected for specific clinical reasons

Even in these situations, the decision should be made at a center with pediatric endocrinology or metabolic bone disease expertise, not in a general outpatient setting.

This Is Not Right For:

• Any adolescent with open epiphyses on imaging
• Girls with a personal or family history of osteosarcoma or other primary bone malignancy
• Teenagers who have received prior skeletal radiation
• Anyone who is pregnant, trying to conceive, or not using reliable contraception
• Girls with primary osteoporosis without fragility fractures who have not tried lifestyle interventions, calcium, vitamin D, and estrogen replacement (if deficient) first
• Adolescents where the underlying cause of bone loss has not been identified and treated

Life-Stage Perspective: The Stakes of Getting This Wrong

A postmenopausal woman starting abaloparatide has a largely static skeleton and decades of established bone loss. An adolescent girl's skeleton is in active construction. Intervening with a PTH analog in that window could theoretically accelerate bone formation in ways that are beneficial, but it could also disrupt normal modeling and remodeling signals in ways that have not been studied. The ACE inhibitor analogy is instructive: drugs that are safe and effective in adults can cause unexpected developmental harm in pediatric populations simply because the underlying physiology is categorically different.

Monitoring, Dosing, and Practical Considerations If Abaloparatide Is Used Off-Label

If, after comprehensive specialist review, abaloparatide is used in an adolescent female, the following monitoring framework reflects standard-of-care extrapolation from adult protocols combined with pediatric bone disease principles.

Dosing

The adult dose is 80 mcg subcutaneously once daily. No weight-based or age-adjusted pediatric dose has been established. Some pediatric endocrinologists use the standard 80 mcg adult dose in older adolescents with closed epiphyses and adult-range body weight, but this is purely empirical.

Baseline and Interval Monitoring

• DXA of lumbar spine and total hip (or total body less head in younger patients) at baseline and every 12 months
• Serum calcium, phosphorus, and creatinine at baseline, 1 month, 3 months, then every 6 months
• 25-hydroxyvitamin D and parathyroid hormone at baseline; ensure vitamin D sufficiency before starting
• Bone turnover markers (P1NP and CTX) at baseline and 3 months to confirm anabolic response; P1NP rises within 1 to 3 months in adult responders and can serve as an early signal
• Urine calcium at baseline if hypercalciuria is a concern (particularly in immobilized patients)
• Pregnancy test before each prescription refill

Duration

The FDA-approved maximum cumulative lifetime duration of abaloparatide plus teriparatide combined is 2 years. This applies to adults; the same limit is generally applied in any off-label adolescent use. After stopping an anabolic agent, antiresorptive therapy is typically initiated to preserve gains, a transition that also lacks pediatric-specific trial data.

Injection Technique and Tolerability

Abaloparatide is injected into the periumbilical abdomen daily. Common side effects in adult women include hypercalciuria, dizziness, nausea, headache, and injection-site reactions. In the ACTIVE trial, 3.7 percent of patients discontinued due to adverse events. Orthostatic hypotension can occur within 4 hours of injection; adolescents should be counseled to sit or lie down for 30 minutes after the first several injections.

The Evidence Gap: What Honest Disclosure Looks Like

Women have been historically underrepresented in clinical trials, and girls under 18 have been almost entirely absent from osteoporosis drug trials. The pediatric evidence gap for abaloparatide is not a minor footnote. It means that every element of how this drug behaves in a developing female skeleton, its PK profile, its effect on growth plates not fully closed, its interaction with pubertal hormones, its long-term safety, is either extrapolated from adults or derived from animal models.

The ACTIVE trial enrolled only postmenopausal women with a mean age of 69. The ACTIVExtend study, which followed participants transitioning to alendronate, had a similar demographic. Neither study included anyone under 50. Applying those results to a 14-year-old requires a leap of biological faith that is not currently supported by data.

"The scarcity of randomized controlled trial data in pediatric populations means that off-label prescribing of bone anabolic agents in adolescents must rest on individualized benefit-risk assessment, not extrapolation from adult guidelines," notes the American Society for Bone and Mineral Research's 2019 position statement on pediatric osteoporosis. That statement does not specifically address abaloparatide (which was newer at the time of publication) but applies directly to PTH analog use in this age group.

The Endocrine Society's guidelines on osteoporosis in premenopausal women, published in 2017, similarly note that anabolic agents should be reserved for severe cases unresponsive to standard therapy, with the caveat that most evidence comes from postmenopausal populations.

Questions to Ask Before Starting Abaloparatide Off-Label in an Adolescent

Before any adolescent girl starts this therapy, the prescribing clinician and family should be able to answer yes to every question on this list:

1. Has a pediatric metabolic bone specialist reviewed the case?
2. Are the growth plates confirmed closed on plain radiograph?
3. Has a primary bone malignancy been excluded clinically and radiographically?
4. Has at least one evidence-based first-line therapy been tried and failed?
5. Is the adolescent using reliable, effective contraception?
6. Has she been counseled specifically about the osteosarcoma boxed warning in language appropriate to her age?
7. Is there a monitoring plan with defined DXA intervals, lab checks, and a stopping rule?
8. Has the transition plan after anabolic therapy been discussed with the prescribing team?

If any answer is no, abaloparatide should not be started.