Evenity vs Forteo: Comparing Anabolic Osteoporosis Treatments

How Romosozumab and Teriparatide Build Bone

These two drugs reach the same goal through opposite biological pathways. Romosozumab blocks sclerostin, a protein that osteocytes release to slow bone formation. By inhibiting sclerostin, romosozumab simultaneously increases bone formation markers and decreases bone resorption markers, a dual effect no other approved agent replicates [1]. Teriparatide mimics parathyroid hormone. When given as a once-daily pulse (rather than continuous exposure), intermittent PTH stimulates osteoblast activity and new bone deposition [2].

The practical difference shows up in biomarker kinetics. Within one month of starting romosozumab, serum P1NP (a formation marker) spikes while CTX (a resorption marker) drops. This "anabolic window" closes by month 6 to 9 as sclerostin-independent resorption catches up [1]. Teriparatide raises both P1NP and CTX from the first month, reflecting coupled bone turnover. That coupled remodeling is why teriparatide needs 18 to 24 months to reach peak BMD effect, while romosozumab front-loads most of its gains into the first 6 months [3].

The 2020 Endocrine Society guideline update notes: "Romosozumab has a unique dual mechanism of action, increasing bone formation while decreasing bone resorption, distinguishing it from all other osteoporosis therapies" [4]. This distinction matters when selecting a drug for patients who need the fastest possible BMD recovery at the hip.

Head-to-Head BMD Data: The STRUCTURE Trial

The STRUCTURE trial (N=436) is the only completed randomized study directly comparing romosozumab and teriparatide [5]. It enrolled postmenopausal women who had been on oral bisphosphonates for at least three years before switching to one of the two anabolic agents for 12 months.

Results favored romosozumab at the total hip. Romosozumab produced a 2.6% gain in total hip BMD versus a -0.2% change with teriparatide (treatment difference 2.8 percentage points, P<0.0001) [5]. At the femoral neck, romosozumab gained 3.2% compared with 0.8% for teriparatide. Lumbar spine results were closer: romosozumab gained 9.8% versus 5.4% for teriparatide [5].

These findings have a specific clinical context. All participants had prior bisphosphonate exposure. That matters because bisphosphonates blunt the early anabolic response to teriparatide but do not appear to reduce the response to romosozumab [6]. If a patient is transitioning off a bisphosphonate, romosozumab may deliver faster hip BMD recovery than teriparatide.

One limitation: STRUCTURE was not powered for fracture endpoints. BMD is a validated surrogate, but the trial cannot tell us whether 2.8 percentage points of extra hip BMD translates into fewer hip fractures.

Fracture Reduction Evidence

Neither drug has been tested against the other in a fracture-endpoint trial. The fracture data for each comes from separate placebo- or active-comparator studies.

For romosozumab, the ARCH trial (N=4,093) randomized postmenopausal women to romosozumab for 12 months followed by alendronate, or to alendronate alone for 24 months [7]. At the primary endpoint, the romosozumab-to-alendronate sequence reduced new vertebral fractures by 48% (6.2% vs 11.9%, P<0.001) and clinical fractures by 27% compared with alendronate alone [7]. The FRAME trial (N=7,180) compared romosozumab to placebo for 12 months, followed by denosumab in both arms. At 12 months, romosozumab reduced new vertebral fractures by 73% versus placebo [8].

For teriparatide, the key Fracture Prevention Trial (N=1,637) showed a 65% reduction in new vertebral fractures and a 53% reduction in nonvertebral fractures compared with placebo over a median 21 months [2]. The VERO trial (N=1,360) compared teriparatide head-to-head against risedronate in women with severe osteoporosis. Teriparatide reduced new vertebral fractures by 56% relative to risedronate at 24 months (5.4% vs 12.0%, P<0.0001) [9]. That trial provided the first evidence that an anabolic agent outperforms an active antiresorptive for fracture prevention.

Dr. Felicia Cosman, professor of medicine at Columbia University, wrote in her 2020 review: "Anabolic-first strategies should be considered for patients at very high fracture risk because starting with bone formation before adding antiresorptive therapy produces larger cumulative BMD gains and potentially greater long-term fracture protection" [10].

Dosing, Administration, and Treatment Duration

Romosozumab is given as two subcutaneous injections of 105 mg each (210 mg total) once monthly for 12 consecutive months. Injections are administered in a healthcare setting or by a trained caregiver. The full course is 12 doses. There is no option to extend beyond 12 months because the anabolic effect wanes as the body produces anti-drug antibodies and resorption re-couples [7].

Teriparatide requires a daily 20 mcg subcutaneous injection self-administered by the patient using a prefilled pen device. The maximum approved treatment duration is 24 months [2]. Most patients are trained on injection technique in one office visit and continue at home.

The difference in injection burden is significant. Twelve clinic visits over a year versus 730 self-injections over two years. Adherence rates reflect this gap. A retrospective claims analysis found that 12-month persistence with romosozumab was 61.4% compared with 32.1% for teriparatide [11]. Missed injections erode cumulative BMD gains, so this adherence advantage has real clinical weight.

Safety and Contraindications

The FDA added a boxed warning to romosozumab's label in 2019 after the ARCH trial showed a numerical imbalance in serious cardiovascular events (2.5% romosozumab vs 1.9% alendronate) [7]. Romosozumab is contraindicated in patients who have had a myocardial infarction or stroke within the preceding year. The AACE 2020 guidelines recommend avoiding romosozumab in patients with "high cardiovascular risk" without specifying a threshold, though they note the absolute event difference was small [12].

Teriparatide carried a boxed warning about osteosarcoma based on rat studies where lifelong high-dose exposure (3 to 58 times the human dose) caused bone tumors [2]. After 15 years of postmarketing surveillance, no causal link to osteosarcoma in humans was confirmed. The FDA removed the osteosarcoma boxed warning from teriparatide's label in 2020 [13]. Teriparatide remains contraindicated in patients with Paget's disease, unexplained alkaline phosphatase elevation, prior radiation to the skeleton, open epiphyses, or pre-existing hypercalcemia.

Common adverse reactions with romosozumab include injection-site reactions (5.2%), arthralgia (12.4%), and headache (5.4%) [8]. For teriparatide, orthostatic hypotension within 4 hours of dosing (reported in about 5% of patients), leg cramps (2.6%), and transient hypercalcemia (11% above normal range) are the most frequent concerns [2].

Cost and Insurance Coverage

Both drugs carry high list prices. As of 2025, romosozumab (Evenity) lists at roughly $1,825 per monthly dose, totaling approximately $21,900 for a 12-month course [14]. Teriparatide (Forteo) lists at about $3,700 per month, though generic teriparatide (available since late 2023) has lowered some out-of-pocket costs to $400 to $900 per month depending on the pharmacy [15].

Medicare Part B covers romosozumab as a physician-administered injectable. Teriparatide, being self-administered, falls under Part D prescription drug plans. Prior authorization is standard for both drugs. Most commercial insurers require documentation of a T-score at or below -2.5, a prior fragility fracture, or failure of oral bisphosphonate therapy before approving either anabolic agent [14].

For patients comparing net cost, the shorter romosozumab course (12 months vs 24 months for teriparatide) can make total out-of-pocket costs comparable or lower, even when the monthly price of romosozumab is higher. The availability of generic teriparatide has shifted this calculation, however, and some patients now pay less for the full 24-month teriparatide course than for 12 months of brand-name romosozumab.

Sequencing: What Comes After the Anabolic Phase

Stopping either drug without transitioning to an antiresorptive leads to rapid bone loss. This is non-negotiable. The 2020 AACE/ACE guideline states: "Following completion of anabolic therapy with teriparatide, abaloparatide, or romosozumab, treatment with an antiresorptive agent is mandatory to maintain or enhance BMD gains" [12].

The two main antiresorptive options are bisphosphonates and denosumab (Prolia). Each has trade-offs.

Bisphosphonates (alendronate or zoledronic acid): Oral alendronate (70 mg weekly) is the most prescribed and least expensive. Zoledronic acid (5 mg IV once yearly) offers better adherence because it is a single annual infusion. The HORIZON trial (N=7,765) showed zoledronic acid reduced hip fractures by 41% versus placebo over 3 years [16]. Head-to-head, zoledronic acid produces greater BMD gains at the hip than oral alendronate, largely driven by superior adherence [17].

Denosumab (Prolia): A subcutaneous injection every 6 months. Denosumab produces larger BMD gains than bisphosphonates over 10 years of continuous use, per the FREEDOM extension data [18]. The trade-off: stopping denosumab causes rebound bone loss and a spike in vertebral fracture risk, so patients must either stay on it long-term or transition to a bisphosphonate before discontinuing [19]. The DATA-Switch study showed that patients who used teriparatide first and then switched to denosumab achieved greater BMD gains than those who used either agent alone [20].

For patients finishing romosozumab, the ARCH trial's protocol used alendronate as the sequel, and the FRAME trial used denosumab. Both sequences preserved and extended BMD gains [7][8]. There is no evidence yet that one antiresorptive sequel is superior to the other after romosozumab specifically.

How Forteo Compares with Tymlos

Abaloparatide (Tymlos) is the other anabolic option. It acts on the same PTH1 receptor as teriparatide but has a modified binding profile that favors the RG conformation, producing slightly less hypercalcemia [21]. The ACTIVE trial (N=2,463) demonstrated that abaloparatide reduced new vertebral fractures by 86% versus placebo at 18 months, compared with 80% for the open-label teriparatide arm in the same study [21]. Nonvertebral fracture reduction was statistically significant for abaloparatide (43% reduction) but not for teriparatide in this trial, though the study was not powered for a direct head-to-head nonvertebral comparison.

Both drugs use daily subcutaneous injections. Both carry 24-month maximum treatment durations. The practical differences: abaloparatide causes less hypercalcemia (3.4% vs 6.4% for teriparatide) and may produce faster BMD gains at the hip in the first 6 months [21]. Generic teriparatide is available; abaloparatide has no generic as of 2025, keeping its list price above $2,000 per month.

Which Drug for Which Patient

The choice between romosozumab and teriparatide depends on three clinical factors.

Fracture site and urgency. If hip fracture risk is the primary concern and the patient is transitioning off a bisphosphonate, romosozumab's superior hip BMD gains in STRUCTURE make it the stronger candidate [5]. If vertebral fracture risk dominates and the patient has not used bisphosphonates recently, teriparatide's 24-month fracture data from VERO support its use [9].

Cardiovascular history. Any patient with a recent MI, stroke, or multiple cardiovascular risk factors should not receive romosozumab per the FDA label [7]. Teriparatide or abaloparatide would be the default anabolic option for these patients.

Patient preference and adherence. Twelve monthly clinic injections suit patients who struggle with daily self-injection. Patients comfortable with daily self-care and those who prefer a home-based regimen may tolerate teriparatide or abaloparatide better. The adherence data favor romosozumab by a wide margin [11].

For patients with T-scores at or below -3.0, multiple prior fractures, or glucocorticoid-induced bone loss, the 2020 AACE guidelines recommend starting with any available anabolic agent before using antiresorptives, rather than the reverse [12]. The specific anabolic chosen should follow the patient-level factors listed above.