Tymlos (abaloparatide) is a prescription injection used to treat osteoporosis in people at high risk for bone fractures. It’s FDA-approved for two groups: postmenopausal women with osteoporosis and men with osteoporosis who have either already broken a bone due to osteoporosis or have multiple risk factors that make fractures likely. It’s also an option for people who haven’t responded to or can’t tolerate other osteoporosis treatments.
How Tymlos Builds Bone
Most osteoporosis drugs work by slowing bone loss. Tymlos takes a different approach: it actively stimulates new bone formation. It’s a synthetic version of a natural protein in your body called parathyroid hormone-related peptide (PTHrP), which plays a role in regulating how bone cells grow and remodel.
When injected daily, Tymlos triggers bone-building cells to ramp up production of new bone tissue. It also increases bone breakdown to a lesser degree, but the net effect strongly favors bone growth. In clinical trials, markers of new bone formation peaked within about one month and stayed elevated throughout treatment, while markers of bone breakdown rose more slowly, peaked around three months, and then returned to baseline by the end of the study. This imbalance toward building rather than breaking is what makes Tymlos an “anabolic” osteoporosis treatment.
How Well It Prevents Fractures
The main clinical trial behind Tymlos, called ACTIVE, tested the drug against a placebo over 18 months. The results were significant: the rate of clinical fractures at any site dropped from 5.9% with placebo to 3.3% with Tymlos. For vertebral fractures specifically, Tymlos reduced the absolute risk by 3.6 percentage points compared to placebo. In practical terms, treating 28 patients with Tymlos for 18 months prevented one additional vertebral fracture that would have otherwise occurred.
How You Take It
Tymlos is a daily self-injection of 80 micrograms, delivered just under the skin of your lower abdomen. You use a prefilled pen similar to what people with diabetes use for insulin. The injection site should be the area around your belly button, but at least two inches away from the navel itself. Most people learn the technique quickly during their first appointment.
Before your first use, the pen needs to be refrigerated between 36°F and 46°F. Once you start using it, you can keep it at room temperature (68°F to 77°F) for up to 30 days. Don’t freeze it or expose it to heat.
Treatment Duration and What Comes After
Tymlos is designed as a time-limited treatment, typically used for up to 18 to 24 months. This isn’t a medication you stay on indefinitely. The bone density gains you achieve during treatment can fade if you don’t follow up with another type of osteoporosis drug afterward.
That follow-up step is critical. After finishing Tymlos, patients are typically started on a bone-preserving medication to lock in the new bone that was built. The most common options are oral bisphosphonates, an intravenous bisphosphonate given once yearly, or a different injectable called denosumab for people who can’t take bisphosphonates. Skipping this transition therapy can mean losing much of the benefit Tymlos provided.
Common Side Effects
Side effects differ somewhat between men and women, but the most frequently reported ones overlap. In postmenopausal women, the most common reactions (occurring in at least 2% of patients) include excess calcium in the urine, dizziness, nausea, headache, heart palpitations, fatigue, upper abdominal pain, and vertigo. In men, the most common reactions include redness, swelling, or pain at the injection site, dizziness, joint pain, bruising, nausea, diarrhea, abdominal bloating, abdominal pain, and bone pain.
Elevated blood calcium is a known concern. In clinical trials, about 3% of patients on Tymlos developed temporarily high calcium levels measured four hours after injection, compared to essentially 0% on placebo. For most people this doesn’t cause symptoms, but it’s something your provider will monitor with periodic blood tests.
Who Should Not Take Tymlos
Tymlos is not appropriate for everyone with osteoporosis. It’s specifically reserved for people at high risk for fractures, meaning those who have already had an osteoporotic fracture or who carry several risk factors. People with conditions that cause abnormally high calcium levels, unexplained elevations in a bone enzyme called alkaline phosphatase, or those who have had radiation therapy involving the skeleton are generally not candidates. It’s also not used in children or young adults whose bones are still growing.
How Tymlos Compares to Forteo
Tymlos is often compared to teriparatide (Forteo), the other daily injectable bone-building osteoporosis drug. The two medications aren’t technically in the same class: Tymlos is modeled after PTHrP, while Forteo is modeled after parathyroid hormone (PTH). But they both activate the same receptor on bone cells and share a similar mechanism. The practical differences come down to side effect profiles, fracture reduction data, and cost, which vary enough that the choice between them is usually individualized based on your health history and how you respond to treatment.