What Is Teriparatide?

1. How does teriparatide build bone?

Parathyroid hormone, or PTH, is the body’s main controller of calcium and phosphate. It acts on bone and on the kidneys, and indirectly increases calcium absorption from the gut. According to the Forteo prescribing information, teriparatide binds the same PTH receptors as the natural hormone, with the same affinity. Forteo is produced in a genetically modified strain of E. coli.

What makes it a bone builder is timing. The same hormone can strengthen or weaken the skeleton depending on whether exposure is brief or constant:

That is why the drug is given as a single daily dose rather than a long-acting formulation. It is a peptide that clears quickly, so each injection produces a brief pulse.

Anabolic for bone, not muscle

Every outcome in teriparatide’s approval trials was bone density or fracture. We found no controlled trial showing that it adds muscle or improves performance. Readers concerned about muscle loss on GLP-1 medicines should treat bone and muscle as separate questions with separate evidence.

2. What did the fracture trials show?

Postmenopausal women

Neer and colleagues’ Fracture Prevention Trial enrolled 1637 postmenopausal women who already had at least one vertebral fracture. They received 20 mcg, 40 mcg or placebo daily, plus calcium and vitamin D, for a median of 21 months. The trial ended early because of the rat tumor finding described in section 6.

BMD means bone mineral density, usually measured by a DXA scan. The higher dose raised density further but did not prevent more fractures and caused more side effects, so only 20 mcg was approved. The label’s analysis puts the 20 mcg arm’s absolute vertebral fracture reduction at 9.3% and the relative reduction at 65%, and reports normal mineralization in bone biopsies from 35 women.

Head to head with risedronate

The VERO trial by Kendler and colleagues compared two osteoporosis drugs using fractures, not just density, as the main outcome. It randomized 1360 women with severe osteoporosis to daily teriparatide 20 mcg or weekly oral risedronate 35 mg for 24 months under double-blind conditions. Lilly funded it.

Men and glucocorticoid users

In Orwoll and colleagues’ trial of 437 men, 20 mcg daily raised spine density by 5.9% and femoral neck density by 1.5% over a median of 11 months. The response did not depend on testosterone status, age or starting density. Fractures were not an outcome, so the male indication is framed as increasing bone mass.

Saag and colleagues compared teriparatide with daily alendronate 10 mg in 428 adults on long-term glucocorticoids for 18 months:

High calcium readings were more frequent with teriparatide in this trial.

3. Does teriparatide help with bone loss during GLP-1 weight loss?

No trial cited here has tested teriparatide in people losing weight with semaglutide, tirzepatide or any other GLP-1 medicine. Its approved use is osteoporosis at high fracture risk, not protecting bone during weight loss in general.

The concern itself has some data behind it. Jensen and colleagues’ 2024 secondary analysis followed 195 adults with obesity and without diabetes. After an 8-week 800-calorie-a-day diet, they were randomized for one year to exercise, liraglutide 3.0 mg daily, both, or placebo.

The hip and spine differences between liraglutide alone and exercise alone were small, 0.013 and 0.016 g/cm² respectively. The study measured density, not fractures, and used liraglutide rather than newer GLP-1 drugs. It suggests that how weight is lost may matter for bone. It does not show that a bone drug is needed or helpful during GLP-1 treatment.

A DXA scan reports bone separately from fat and lean tissue, so the same scan used to follow body composition can also give bone density readings. Whether a person needs osteoporosis treatment depends on their own fracture risk, which a clinician assesses.

4. Is teriparatide FDA approved and legal?

Yes. The current label approves it for three groups, each limited to people at high fracture risk or who have failed or cannot tolerate other osteoporosis treatment:

• postmenopausal women with osteoporosis;
• men with primary or hypogonadal osteoporosis, to increase bone mass;
• adults with osteoporosis linked to ongoing glucocorticoid use of at least 5 mg a day of prednisone or an equivalent.

It is not approved for children. Several teriparatide products are now on the US market:

The trial data on this page come from Forteo.

The 2-year limit became conditional

Controlled substance and sport status

Teriparatide is a prescription drug but is not among the anabolic steroids listed in Schedule III, 21 CFR 1308.13. It does not appear by name on the WADA 2026 Prohibited List. That list’s growth-factor class, S2.3, also covers unnamed factors that affect muscle, tendon or ligament protein synthesis or regeneration, and PTH analogs are not among its examples. Athletes should check with their anti-doping body rather than assume a compound is permitted.

A vial marketed online as research-grade teriparatide has not been through FDA review, so nobody has confirmed what it contains, how much, or whether it is sterile.

5. Teriparatide dosage and half-life, as labeled

The labeled dose is 20 mcg injected under the skin of the thigh or abdomen once a day. Each Forteo pen holds 28 daily doses and is thrown away 28 days after first use. It must be kept refrigerated except while injecting. The label recommends calcium and vitamin D supplements if dietary intake is too low, and advises taking the first doses where the person can sit or lie down.

Pharmacokinetic values from the FDA label:

Lilly did not run dedicated metabolism studies. The label attributes breakdown to nonspecific liver enzymes, with the kidneys handling most of the elimination.

The effect on blood calcium outlasts the drug. Calcium begins rising about 2 hours after a dose, peaks at 4–6 hours with a median increase of 0.4 mg/dL, and returns to baseline by 16–24 hours. A half-life curve therefore describes the drug level, not how long its effects last.

6. Side effects and the osteosarcoma question

From boxed warning to standard warning

In two-year rat studies, teriparatide caused osteosarcoma, a bone cancer, in a dose- and duration-dependent way. Rates reached 40–50% in high-dose groups exposed to 3 to 60 times human levels. Monkeys treated for 18 months and followed for 3 more years developed no bone tumors.

Forteo therefore launched with a boxed warning, a 2-year lifetime cap and required cancer surveillance, as Krege and colleagues’ history describes. The human surveillance results led FDA to remove the boxed warning on November 16, 2020:

For scale, osteosarcoma occurs in about 2.5 per million US adults aged 40 or older each year. The label still lists the warning, notes limited data beyond 2 years, and says to avoid teriparatide in people with higher baseline risk: open growth plates, Paget’s disease or other metabolic bone disease besides osteoporosis, bone metastases or past skeletal cancer, prior radiation to the skeleton, or inherited conditions that predispose to osteosarcoma.

Severe allergic reactions, added in 2026

FDA asked Lilly in April 2026 to add hypersensitivity information to labeling for parathyroid hormone products, and the S-059 update was approved on August 3, 2026. The label now lists anaphylaxis, angioedema (deep swelling) and hives reported with PTH analogs. The drug should be stopped if a reaction occurs, and stopped permanently after a severe one. A history of severe hypersensitivity to teriparatide or its ingredients is now the only contraindication.

Common effects

About 5% of healthy volunteers in short studies had brief dizziness from low blood pressure on standing, usually within 4 hours of an early dose. Pooled trial rates, with 691 people per group:

Against alendronate in glucocorticoid users, nausea, pneumonia and shingles were more frequent with teriparatide.

7. Calcium, interactions and monitoring

Because each dose raises blood calcium for several hours, the label’s calcium findings are the main practical safety point. In trials, at least one high calcium reading 4–6 hours after a dose occurred in 11% of women and 6% of men, against 2% and 0% on placebo. Repeat testing confirmed it in 3% of women and 1% of men. Values over 13 mg/dL have been reported since approval.

Other points from the label:

• Hypercalcemic disorders. Avoid in people with conditions such as primary hyperparathyroidism.
• Calciphylaxis. Serious calcium deposits in small skin blood vessels have been reported. Risk factors include autoimmune disease, kidney failure, and warfarin or systemic corticosteroid use.
• Kidney stones. Rates matched placebo, but people with active or recent stones were not studied.
• Uric acid. Levels rose above normal in 3% versus 1% on placebo, without more gout.
• Digoxin. The calcium rise may make digitalis toxicity more likely.
• Diuretics. Hydrochlorothiazide and IV furosemide caused only small changes in calcium.
• Pregnancy and breastfeeding. No human data exist. The label says to consider stopping when pregnancy is recognized and not to breastfeed.
• Overdose. Accidental doses of up to 800 mcg, a whole pen, caused nausea, weakness and low blood pressure, with no reported deaths.
• Antibodies. About 3% of women in the pivotal trial developed them, without any effect on calcium or density response.

GLP-1 medicines are not among the interactions the label highlights, and no study cited here examined the combination. Calcium readings are most informative when the timing relative to the last injection is known, since the 4–6 hour peak differs from a level drawn the next morning.

8. Does teriparatide speed injury recovery?

Teriparatide is promoted online for healing fractures and tendons. Controlled human trials give mixed or null results:

A 2021 meta-analysis by Eastman and colleagues found better function with PTH analogues but no change in healing rate or pain. Most trials enrolled older people with osteoporosis, so evidence in younger adults is weaker. Muscle and ligament injuries have not been tested in any controlled human trial we could find. Unlike BPC-157, teriparatide is an approved drug, but injury healing is not one of its approved uses.

9. What happens after stopping, and what can you track?

Bone gained on teriparatide does not hold on its own. In the DATA-Switch extension by Leder and colleagues, women who moved from 2 years of teriparatide to denosumab kept gaining, reaching an 18.3% spine density increase at 4 years. Women who moved the other way lost bone, especially at the hip and wrist. Only 77 women were analyzed, but the authors concluded the order of treatments deserves attention.

The outcomes the trials used are the ones worth recording:

• Bone density. DXA results at the spine and hip, with the scan date and the same scanner where possible.
• Fractures. Any new fracture, including vertebral fractures found on imaging.
• Calcium. Blood calcium values with the time since the last injection.
• Dose log. Injection dates and times, pen start dates for the 28-day discard rule, and missed doses.
• Symptoms. Dizziness after early doses, joint pain, leg cramps, nausea and any allergic reaction.

If you are also on a GLP-1 medicine, logging weight and body composition alongside these makes later DXA results easier to interpret. A tracking log can organize that history for a clinician; it cannot show whether teriparatide changed your fracture risk.

10. Teriparatide FAQ

• What is teriparatide used for?

  The FDA label approves it for osteoporosis at high fracture risk in postmenopausal women, in men with primary or hypogonadal osteoporosis, and in adults with osteoporosis linked to long-term glucocorticoid use. Healing fresh fractures, tendon repair and muscle growth are not approved uses.

• Is teriparatide legal?

  In the US it is a prescription drug. It is not a scheduled anabolic steroid under federal law, and it is not named on the 2026 WADA Prohibited List, although that list's growth-factor class is open-ended. Products sold as research peptides are not FDA-approved medicines.

• What are the side effects of teriparatide?

  In pooled trials, joint pain, nausea, dizziness and leg cramps were somewhat more common than on placebo. The label also warns about transient high blood calcium, dizziness on standing after early doses, calciphylaxis, severe allergic reactions and the osteosarcoma finding from rat studies.

• How long does teriparatide stay in your system?

  Per the label, its serum half-life is about 1 hour and it is no longer measurable within 3 hours of an injection. The calcium rise it triggers lasts longer, peaking 4 to 6 hours after a dose and returning to baseline by 16 to 24 hours.

• Does teriparatide still cause cancer?

  Rats given teriparatide for two years developed osteosarcoma, a bone cancer. Large human surveillance studies did not find more osteosarcoma than expected, which is why FDA removed the boxed warning in 2020. The label still lists the risk and advises avoiding the drug in people with higher baseline risk.

• Can teriparatide be used with semaglutide or tirzepatide?

  No study cited here tested the combination, so there is no evidence on whether it changes bone outcomes during GLP-1 weight loss. The interactions the label highlights involve digoxin and diuretics. Anyone weighing both should do so with the prescriber who manages their bone health.

• Does teriparatide build muscle?

  No controlled trial has shown that it builds muscle or improves athletic performance. It is called anabolic because it builds bone. Its trial outcomes were bone density and fractures.

• Can you take teriparatide for more than 2 years?

  Before November 2020 the label advised against more than 2 years in a lifetime. The current label says longer use should only be considered when fracture risk remains high or becomes high again, and it notes limited data beyond 2 years.

11. Sources