Medications for Osteoporosis: Bisphosphonates, Denosumab, and Beyond

The Treatment Gap

Despite the availability of effective medications that reduce fracture risk by 30-70%, osteoporosis remains dramatically undertreated. Studies consistently show that fewer than 20% of patients who experience an osteoporotic fracture are started on bone-protective medication within the following year. Even among patients who are prescribed osteoporosis treatment, adherence rates drop significantly within the first 12 months.

Part of this treatment gap stems from patient concerns about medication side effects, some of which have been amplified beyond their actual clinical significance. This article provides a balanced, evidence-based overview of the major drug classes used to treat osteoporosis, including their mechanisms of action, fracture reduction efficacy, side effects, and key clinical considerations.

Anti-Resorptive Medications

Anti-resorptive medications work by reducing bone resorption — the process by which osteoclasts break down existing bone. By slowing resorption without proportionally reducing bone formation (at least initially), these drugs shift the remodeling balance toward net bone preservation.

Bisphosphonates

Bisphosphonates are the most widely prescribed class of osteoporosis medication and have the longest track record of clinical use. They bind to hydroxyapatite in bone mineral and are taken up by osteoclasts during bone resorption, where they inhibit an enzyme (farnesyl pyrophosphate synthase) essential for osteoclast function and survival.

Currently available bisphosphonates include:

• Alendronate (Fosamax): Oral, taken weekly. The Fracture Intervention Trial (FIT) demonstrated a 47% reduction in spine fractures and a 51% reduction in hip fractures over 3 years in women with existing vertebral fractures.
• Risedronate (Actonel): Oral, taken weekly or monthly. The VERT and HIP trials showed approximately 41% reduction in vertebral fractures and 30% reduction in non-vertebral fractures over 3 years.
• Ibandronate (Boniva): Oral (monthly) or intravenous (quarterly). The BONE trial demonstrated vertebral fracture reduction, but ibandronate has not demonstrated hip fracture reduction in clinical trials, which limits its use compared to alendronate and risedronate.
• Zoledronic acid (Reclast): Intravenous, given once yearly. The HORIZON Pivotal Fracture Trial showed a 70% reduction in vertebral fractures, 41% reduction in hip fractures, and 25% reduction in non-vertebral fractures over 3 years. The annual IV dosing eliminates concerns about oral absorption and gastrointestinal tolerability.

Bisphosphonate Side Effects and Concerns

Gastrointestinal effects: Oral bisphosphonates can cause esophageal irritation, reflux, and, rarely, esophageal ulcers. To minimize this risk, they must be taken on an empty stomach with a full glass of water, and the patient must remain upright for at least 30 minutes after taking the dose. Patients with esophageal disorders (stricture, achalasia, inability to remain upright) should not take oral bisphosphonates and may be better served by IV zoledronic acid or an alternative drug class.

Osteonecrosis of the jaw (ONJ): This is the side effect that receives the most public attention, and its risk is frequently misunderstood. In patients receiving oral bisphosphonates for osteoporosis, the incidence of ONJ is estimated at approximately 1 in 10,000 to 1 in 100,000 patient-years — extremely rare. The much higher rates of ONJ reported in the literature occur primarily in cancer patients receiving high-dose intravenous bisphosphonates (at doses 10-12 times higher than those used for osteoporosis) for metastatic bone disease. Dental extractions and invasive dental procedures are the most common precipitating events. Good dental hygiene and addressing dental issues before starting bisphosphonate therapy are reasonable preventive measures.

Atypical femoral fractures (AFF): Prolonged bisphosphonate use (typically beyond 5 years) has been associated with a rare pattern of fracture in the subtrochanteric or femoral shaft — called atypical femoral fractures. These fractures are thought to result from over-suppression of bone remodeling, which impairs the body's ability to repair microdamage. The absolute risk is low (approximately 3-50 per 100,000 patient-years with prolonged use), and it must be weighed against the much larger number of typical osteoporotic fractures prevented by treatment. However, this risk is the primary rationale for bisphosphonate "drug holidays" — temporary discontinuation after 3-5 years of treatment in patients at moderate (not high) fracture risk.

Denosumab (Prolia)

Denosumab is a fully human monoclonal antibody that binds RANKL, the cytokine that drives osteoclast differentiation and activation. By neutralizing RANKL, denosumab potently inhibits bone resorption. It is administered as a subcutaneous injection every 6 months.

The FREEDOM trial demonstrated that denosumab reduced vertebral fractures by 68%, hip fractures by 40%, and non-vertebral fractures by 20% over 3 years in postmenopausal women with osteoporosis. Long-term extension data (up to 10 years) have shown sustained increases in bone density and maintained fracture reduction.

Key considerations:

• Rebound bone loss on discontinuation: Unlike bisphosphonates, which remain in bone for years after discontinuation, denosumab's effects reverse rapidly when the drug is stopped. Bone turnover markers can rebound to above pre-treatment levels within 3-6 months, and bone density can decline significantly — in some cases below pre-treatment levels. Most concerning, there have been reports of multiple vertebral fractures occurring after denosumab discontinuation. For this reason, if denosumab is stopped, transition to an alternative anti-resorptive (typically a bisphosphonate) is strongly recommended to prevent rebound bone loss.
• Hypocalcemia: Because denosumab potently suppresses bone resorption (which releases calcium into the blood), patients must have adequate calcium and vitamin D intake before and during treatment. Hypocalcemia is more common in patients with chronic kidney disease or vitamin D deficiency.
• ONJ and AFF: As with bisphosphonates, rare cases of ONJ and atypical femoral fractures have been reported with denosumab, though the absolute risks appear similar to those seen with bisphosphonates at osteoporosis doses.

Selective Estrogen Receptor Modulators (SERMs)

Raloxifene (Evista) is the primary SERM used for osteoporosis treatment. It acts as an estrogen agonist in bone (reducing resorption) and an estrogen antagonist in breast and uterine tissue. The MORE trial demonstrated a 30-50% reduction in vertebral fractures with raloxifene, but it has not been shown to reduce hip or non-vertebral fractures. It also reduces the risk of invasive breast cancer, which may make it a useful option for women at risk for both osteoporosis and breast cancer. Side effects include an increased risk of venous thromboembolism and hot flashes.

Anabolic Medications

Anabolic agents stimulate bone formation, representing a fundamentally different approach than anti-resorptive drugs. They are generally reserved for patients with severe osteoporosis, very high fracture risk, or inadequate response to anti-resorptive therapy.

Teriparatide (Forteo)

Teriparatide is a recombinant fragment of parathyroid hormone (PTH 1-34). When given as a daily subcutaneous injection, intermittent PTH exposure preferentially stimulates osteoblast activity and new bone formation. (This is distinct from the continuous PTH elevation seen in hyperparathyroidism, which stimulates bone resorption.)

In the pivotal trial, teriparatide reduced vertebral fractures by 65% and non-vertebral fractures by 53% over a median treatment duration of 19 months in postmenopausal women with severe osteoporosis. Treatment is limited to 2 years (per the original label, based on osteosarcoma findings in rat studies, though this risk has not been confirmed in humans and labeling has been updated in some countries). After completing teriparatide, patients should transition to an anti-resorptive agent to maintain the bone density gains.

Abaloparatide (Tymlos)

Abaloparatide is a synthetic analog of parathyroid hormone-related protein (PTHrP). Like teriparatide, it is administered as a daily subcutaneous injection and stimulates bone formation. The ACTIVE trial demonstrated an 86% reduction in vertebral fractures and a 43% reduction in non-vertebral fractures over 18 months. Abaloparatide may produce a somewhat greater increase in bone density and a more favorable ratio of bone formation to resorption compared to teriparatide, though direct head-to-head fracture data are limited. Treatment is also limited to 2 years, followed by transition to an anti-resorptive.

Romosozumab (Evenity)

Romosozumab is a monoclonal antibody against sclerostin, a protein produced by osteocytes that inhibits bone formation. By blocking sclerostin, romosozumab has a dual mechanism: it stimulates bone formation and simultaneously reduces bone resorption. This results in rapid and substantial increases in bone density.

The FRAME trial showed a 73% reduction in vertebral fractures over 12 months with romosozumab compared to placebo, followed by further fracture reduction when patients transitioned to denosumab. The ARCH trial compared romosozumab followed by alendronate versus alendronate alone and demonstrated superior fracture reduction with the romosozumab-first sequence.

Key considerations:

• Treatment duration is limited to 12 months (the anabolic effect of romosozumab wanes with continued use as sclerostin levels adapt).
• Transition to an anti-resorptive after 12 months is essential to maintain bone density gains.
• The ARCH trial noted a numerical increase in cardiovascular events (myocardial infarction, stroke) in the romosozumab group compared to the alendronate group during the first 12 months. As a result, romosozumab carries a boxed warning and should not be used in patients with recent cardiovascular events. However, this signal was not seen in the FRAME trial (which compared to placebo), and the cardiovascular risk question remains an area of active investigation.

Treatment Sequencing

An emerging concept in osteoporosis management is that the order in which medications are used matters. Traditional practice has been to start with an anti-resorptive (bisphosphonate or denosumab) and switch to an anabolic agent only if fractures continue or bone density does not improve. However, growing evidence suggests that starting with an anabolic agent in high-risk patients and then transitioning to an anti-resorptive ("build first, then maintain") may produce greater long-term bone density gains and better fracture outcomes than the reverse sequence.

The DATA-Switch study compared teriparatide-to-denosumab versus denosumab-to-teriparatide sequences and found that the anabolic-first approach resulted in greater bone density gains at both the spine and hip after 4 years. This has led several expert panels, including the Endocrine Society and the American Association of Clinical Endocrinology, to recommend considering anabolic-first therapy for patients at very high fracture risk (e.g., those with recent fracture, very low T-scores, or multiple fractures).

How Long to Treat?

Osteoporosis is a chronic condition, and the duration of treatment is an important clinical consideration:

• Bisphosphonates: After 3-5 years of oral bisphosphonate therapy (or 3 years of IV zoledronic acid), reassessment is recommended. For patients at moderate risk, a drug holiday (temporary discontinuation with monitoring) may be appropriate. For patients at high risk (T-score below -2.5 at the hip, history of hip or vertebral fracture), continuation of therapy is generally recommended.
• Denosumab: There is no defined maximum treatment duration. Long-term extension data support safety and efficacy out to 10 years. However, if discontinuation is considered, transition to a bisphosphonate is critical to prevent rebound bone loss.
• Anabolic agents: Teriparatide and abaloparatide are used for up to 2 years; romosozumab for up to 12 months. All should be followed by anti-resorptive therapy.

Making Treatment Decisions

The choice of medication should be individualized based on several factors:

1. Severity of osteoporosis and fracture risk: Patients at very high risk may benefit from anabolic-first therapy, while those at moderate risk may be appropriately managed with bisphosphonates.
2. Patient preferences and adherence concerns: Options range from daily injections (teriparatide, abaloparatide) to weekly oral pills (alendronate) to once-yearly infusions (zoledronic acid) to twice-yearly injections (denosumab). The medication that a patient will actually take consistently is better than a theoretically superior option that is abandoned.
3. Comorbidities: Renal impairment limits bisphosphonate use (contraindicated with GFR below 30-35 mL/min). Cardiovascular history may influence romosozumab decisions. Esophageal disease may preclude oral bisphosphonates.
4. Cost and insurance coverage: Bisphosphonates (particularly generic alendronate) are inexpensive. Denosumab, teriparatide, abaloparatide, and romosozumab are significantly more costly, though patient assistance programs and insurance coverage can mitigate this.

The Bottom Line

Effective osteoporosis medications exist, and they substantially reduce fracture risk. The rare side effects that receive outsized attention — osteonecrosis of the jaw and atypical femoral fractures — must be understood in context: the absolute risk of these complications is far lower than the absolute risk of osteoporotic fractures in an untreated patient with established osteoporosis. The biggest risk for most patients with osteoporosis is not a medication side effect — it is not being treated at all.