Tymlos (Abaloparatide): How It Works and Differs From Forteo
Tymlos is a bone-building osteoporosis drug whose active part, abaloparatide, is a lab-made chain of 34 amino acids. It is shaped after PTHrP, a cousin of parathyroid hormone first found in cancer cells. That is the main way it differs from Forteo, an exact copy of the start of parathyroid hormone itself. Both turn the same lock on bone cells, the PTH1 receptor.
In the US, both need a prescription and are approved for osteoporosis at high fracture risk. One big trial, ACTIVE, gave women either drug or a placebo, yet it was never built to say which drug prevents more fractures. The page below walks through the hormone, the receptor and the trial.
Key facts
What it is: Abaloparatide, a lab-made peptide of 34 amino acids patterned on PTHrP(1-34), sold in the US as Tymlos.
Status, checked 9 November 2026: A US prescription drug for women past menopause and for men with osteoporosis at high fracture risk. No generic is listed.
How it differs from teriparatide: Forteo copies PTH exactly. Abaloparatide is 76% like PTHrP and 41% like PTH.
Shared target: The PTH1 receptor on bone cells, which both drugs switch on.
What no trial has shown: That either drug prevents more fractures than the other.
Sources: Tymlos prescribing information, revised August 2026; Drugs@FDA, NDA 208743 (Tymlos); openFDA search for abaloparatide applications; ACTIVE trial, JAMA 2016
What is abaloparatide made of?
Abaloparatide is a chain of 34 amino acids that chemists build link by link. The Tymlos label calls it a synthetic peptide and an analog of PTHrP(1-34). That means it is shaped after the first 34 links of PTHrP, but with changes. It shares 76% of those links with PTHrP and 41% with the first 34 links of PTH.
Two unusual details. Near the end of the chain sits Aib, a building block that is not one of the 20 standard amino acids. The last link also carries an amide cap, written NH2 in the label. Its formula is C174H300N56O49, and one molecule weighs 3,961 daltons. Forteo's teriparatide is a little heavier, at 4,117.8 daltons.
Built, not grown. Teriparatide is made by E. coli bacteria that carry the human gene, as our Forteo article shows. The label calls abaloparatide synthetic, which means it is made by chemistry rather than grown in cells. Tymlos comes as a clear, colorless liquid. That sets it apart from the many research peptides sold as dry powder, which is the case our peptide reconstitution calculator was made for.
The body notices it. In the women trial, 41% of people on Tymlos made antibodies against abaloparatide, and 26% made antibodies that block it. The label says these antibodies did not seem to change bone density, fracture results or side effects.
Sources: Tymlos prescribing information, revised August 2026; Forteo prescribing information, revised August 2026
What is PTHrP, and where did it come from?
PTHrP, short for parathyroid hormone-related protein, was found by chasing a cancer problem. Lung cancer and some other cancers often drive blood calcium too high. Doctors call this humoral hypercalcemia of malignancy. Something made by the tumors was acting on bone and kidney, so researchers went looking for it.
The 1987 finds. One team purified a PTH-like protein from a human lung cancer cell line called BEN. Eight of its first 16 building blocks matched human PTH. Yet the cells carried the PTH gene without reading it. So a different gene had to be making the protein. The same year, a second report in Science cloned that gene. It coded for a mature protein of 141 amino acids, which looked like PTH only at its start.
Not only a cancer signal. The cloning authors guessed that this new hormone might matter in normal calcium handling too. A 2008 receptor study draws the line this way: PTH works as a hormone carried in the blood, while PTHrP works more locally, near the cells that make it.
An early surprise. Also in 1987, a lab made the first 34 links of PTHrP and tested them in dishes. That piece was 2 to 4 times as strong as PTH(1-34) at raising cAMP, a messenger inside cells. But it had only 6% of the strength of cow PTH(1-34) at breaking down bone in a dish.
Sources: PTHrP gene cloned, Science 1987; PTHrP purified from lung cancer cells, PNAS 1987; First synthetic PTHrP fragments, Science 1987; Receptor shapes for PTH and PTHrP, 2008
How does Tymlos work?
Tymlos works by turning on PTH1, a receptor found on bone cells. The label calls abaloparatide an agonist, which means a key that turns this lock. Turning it starts the cAMP signal inside the cell. Bone-forming cells, called osteoblasts, then lay down new bone on both the spongy inner bone and the hard outer shell.
Short and sharp. Half of the abaloparatide in the blood is gone in about an hour, much like teriparatide. Brief action on this receptor favors building, while nonstop action favors breakdown. Our Forteo explainer covers that timing story in full, so we do not repeat it here.
What the markers show. In women on Tymlos, a blood marker of bone building rose to 93% above the starting level by month 1. A marker of bone breakdown peaked lower, at 26% above the start in month 3, and was back to the starting level by month 18. In rats and monkeys, bone mass and strength went up.
Sources: Tymlos prescribing information, revised August 2026; Abaloparatide receptor selectivity, 2016
Why might abaloparatide act differently at the receptor?
Researchers think the answer may lie in the shape of the lock. Lab studies describe two shapes of the PTH1 receptor. In the RG shape, the receptor is hooked to its signal partner inside the cell, a G protein. In the R0 shape, it is unhooked. A 2008 study found that PTH and PTHrP grip RG about equally. PTH grips R0 better, so its signal can add up to more over time.
Faster on, faster off. In the same cell work, a PTHrP fragment bound the receptor more slowly and let go sooner than PTH(1-34). Its cAMP signal faded faster, with a half-life of about 1 hour against about 2. One building block made a big difference: spot 5 in the chain, which is isoleucine in PTH and histidine in PTHrP. The Tymlos label shows histidine at spot 5 too, though that paper did not test abaloparatide.
The 2016 test on abaloparatide. A follow-up study put abaloparatide itself through these tests. It favored RG more than PTH(1-34) did, and its cAMP signals in cells were shorter. Other lab and animal work had linked strong R0 binding to longer calcium rises. So the hope was more bone building with less breakdown and less high calcium.
Plausible, not proven. The 2016 authors called their result a plausible mechanism, and the animal data only suggested a benefit. Two of the five authors worked for Radius Health, which developed Tymlos. None of this was measured as a fracture result in people. It is a research idea that may help explain trial differences, not a proven edge.
Sources: Receptor shapes for PTH and PTHrP, 2008; Abaloparatide receptor selectivity, 2016; Tymlos prescribing information, revised August 2026
What sets abaloparatide apart from teriparatide?
Tymlos and Forteo share a target and a disease, but almost everything else on paper is different. The table puts their labels and records side by side. It compares facts, not how well either works for a person.
| Feature | Abaloparatide (Tymlos) | Teriparatide (Forteo) |
|---|---|---|
| Drug inside | Abaloparatide | Teriparatide |
| Hormone it is based on | PTHrP, the PTH-related peptide | PTH, parathyroid hormone |
| How close a copy | 76% match to the start of PTHrP, 41% match to the start of PTH | An exact match to the first 34 of the 84 links in PTH |
| How it is made | Built by chemists (the label calls it synthetic) | Grown in E. coli bacteria given the human recipe |
| Weight of one molecule | 3,961 daltons | 4,117.8 daltons |
| Lock it turns | PTH1 receptor | PTH1 receptor |
| Receptor shape it leans toward in cell tests | RG, with shorter signals | Binds R0 more than abaloparatide does |
| Half gone from the blood | In about 1 hour | In about 1 hour |
| First FDA approval | 28 April 2017 | 26 November 2002 |
| Uses on the US label | Women past menopause; men (bone density wording) | Women past menopause; men; steroid-linked osteoporosis |
| Boxed warning came off | December 2021 | November 2020 |
| Use past 2 years in a lifetime | Not recommended | Only considered if fracture risk stays high |
| Generic versions in the US | None listed | Several (see our Forteo page) |
| Name in the EU | Eladynos (2022) | Forsteo (2003) |
Tymlos won FDA approval about 14 and a half years after Forteo. Its label kept the flat 2-year lifetime limit even after Forteo dropped it in 2020.
Sources: Tymlos prescribing information, revised August 2026; Forteo prescribing information, revised August 2026; Drugs@FDA, NDA 208743 (Tymlos); Drugs@FDA, NDA 021318 (Forteo); openFDA search for abaloparatide applications; EMA page for Eladynos; EMA page for Forsteo; Receptor shapes for PTH and PTHrP, 2008; Abaloparatide receptor selectivity, 2016
What did the ACTIVE trial find?
The ACTIVE trial found that abaloparatide cut new spine fractures sharply compared with placebo. It ran from March 2011 to October 2014 at 28 sites in 10 countries. It enrolled 2,463 women past menopause with osteoporosis, at a mean age of 69. For 18 months they got abaloparatide, a placebo (a dummy treatment) or teriparatide.
A partly open trial. Abaloparatide and placebo were double blind, so nobody knew who got which. Teriparatide came only in its own trademarked pen, so it was given open label, and everyone knew who was on it. The main goal compared abaloparatide with placebo alone.
| Result | Placebo | Abaloparatide | Teriparatide |
|---|---|---|---|
| New spine fractures (main goal) | 4.22% | 0.58% | 0.84% |
| Other fractures (nonvertebral) | 4.7% | 2.7% | 3.3% |
| High blood calcium at any check | Not the comparison | 3.4% | 6.4% |
| Stopped the study for side effects | 6.1% | 9.9% | 6.8% |
Reading the numbers. New spine fractures fell from 30 women on placebo to 4 on abaloparatide. The Tymlos label rounds this to 4.2% and 0.6%, an 86% relative drop. Teriparatide also beat placebo, with 6 women. These are trial averages, not promises for any one person.
After the trial. Women from both blinded groups then switched to alendronate, another osteoporosis drug. By month 25, new spine fractures stood at 0.6% in the former Tymlos group and 4.4% in the former placebo group. That number mixes two drugs, so it is not a Tymlos-only result.
Sources: ACTIVE trial, JAMA 2016; ACTIVE abstract, PubMed 27533157; Tymlos prescribing information, revised August 2026
What could the ACTIVE trial not answer?
Nobody has shown that Tymlos is better than Forteo at preventing fractures. ACTIVE was the only big trial with both drugs, and comparing them on spine fractures was not one of its goals. The authors explain why. With the rates they saw, 0.58% against 0.84%, a fair test would have needed about 22,000 women in each group.
What the trial did compare. High blood calcium was a planned safety check between the two. It showed up in 3.4% on abaloparatide and 6.4% on teriparatide. That fits the receptor idea above, but it does not prove it. Bone density rose more on abaloparatide at the total hip and the femoral neck, the top of the thigh bone. At the lower spine after 18 months, the gap was not significant.
A tempting number. Major osteoporotic fractures, a group that includes wrist, upper arm and hip breaks, were 1.5% on abaloparatide and 3.1% on teriparatide. The paper labels that comparison exploratory, which means it can raise a question but cannot settle one.
The fine print. The authors warn that the open-label arm could tilt side effect reports, and that only a few fractures happened in any group. Radius Health funded the study, and several authors worked there. So the honest summary is simple: both beat placebo, and no study crowns a winner. The right choice for one patient belongs to that patient and their doctor.
Sources: ACTIVE trial, JAMA 2016; ACTIVE abstract, PubMed 27533157
Is Tymlos approved for men?
Yes. On 19 December 2022 the FDA approved a new use: to raise bone density in men with osteoporosis at high fracture risk. The wording matters. For women, the label claims a lower risk of spine and nonspine fractures. For men, it only says it raises bone density, because that is what the men trial measured.
The ATOM trial. It put 228 men aged 40 to 85 on abaloparatide or placebo, two to one, for 12 months. Spine bone density rose 8.48% on abaloparatide and 1.17% on placebo. Hip and femoral neck density also rose more. Four of the paper's authors worked at Radius Health.
Sources: FDA letter adding the men indication, 2022; Tymlos prescribing information, revised August 2026; ATOM trial in men, JBMR 2022; Drugs@FDA, NDA 208743 (Tymlos)
What are the side effects of Tymlos?
The side effects of Tymlos most often listed are extra calcium in the urine, dizziness, nausea, headache and a pounding heartbeat. The table shows the women trial, 822 on Tymlos and 820 on placebo. Each row was more common on Tymlos and hit at least 2% of users.
| Effect | Tymlos | Placebo |
|---|---|---|
| Extra calcium in the urine | 11% | 9% |
| Dizziness | 10% | 6% |
| Nausea | 8% | 3% |
| Headache | 8% | 6% |
| Pounding heartbeat (palpitations) | 5% | 0.4% |
| Tiredness | 3% | 2% |
| Upper belly pain | 3% | 2% |
| Spinning feeling (vertigo) | 2% | 2% |
Heart rate and blood pressure. Tymlos can speed the heart for a while. In a heart study, the rate rose within 15 minutes and settled in about 6 hours. A drop in blood pressure on standing can happen too, usually within 4 hours of taking it. Signs include dizziness, a racing heart and nausea.
Calcium and uric acid. Four hours after use, 3% of women on Tymlos had high blood calcium, against 0.1% on placebo. Uric acid rose above normal at least once in 25% of women on Tymlos and 6% on placebo, without more gout. Kidney stones were reported in 2.1% against 1.7%.
In men. The men trial listed skin redness, swelling and pain where it goes in, plus dizziness and joint pain, as the most common. In ACTIVE, 9.9% of women on abaloparatide stopped for side effects, against 6.8% on teriparatide. Nausea, dizziness, headache and palpitations were the usual reasons.
The five label warnings:
- Allergic reactions, including anaphylaxis, swelling under the skin and hives. Added in August 2026 for parathyroid hormone products after an FDA letter that April.
- Osteosarcoma, from the rat study below.
- Low blood pressure on standing.
- High blood calcium. Not recommended for people who already have it or have a disorder such as primary hyperparathyroidism.
- Extra calcium in the urine, and kidney stones.
The label says Tymlos is not meant for women who could become pregnant. Weighing these risks for one patient is a job for that patient and their care team.
Sources: Tymlos prescribing information, revised August 2026; FDA letter on the 2026 Tymlos allergy update; ACTIVE trial, JAMA 2016
What did the rat study show, and why did the boxed warning go?
In a 2-year rat study, abaloparatide raised the rate of osteosarcoma, a cancer that starts in bone. The rats got 4 to 28 times the exposure people get. Untreated rats had a rate of 0% to 2%. At the top level it reached 87% of males and 62% of females. The label says the meaning for humans is uncertain.
From a box to a warning. The April 2017 launch label opened with a boxed warning about this risk. The December 2021 label lists that boxed warning as removed, and Drugs@FDA dates the change to 22 December 2021. Osteosarcoma is still one of the warnings. The label says it is unknown whether Tymlos causes it in people. Cases have been reported with drugs of this family after approval, but observational research in humans has not found the risk to be higher.
Who the label says should avoid it. Children and young adults with growth plates still open; Paget's disease or another metabolic bone disorder other than osteoporosis; bone metastases or a past skeletal cancer; past radiation therapy that reached the skeleton; and inherited disorders that make osteosarcoma more likely. Forteo has its own rat history, told in our Forteo article.
Sources: Tymlos prescribing information, revised August 2026; Tymlos launch label, April 2017; Tymlos label, December 2021 revision; Drugs@FDA, NDA 208743 (Tymlos)
Is Tymlos still approved in 2026?
Yes. On 9 November 2026, Drugs@FDA lists Tymlos as a prescription drug under NDA 208743. Its newest label change, the allergy warning, was approved on 3 August 2026. That FDA letter is addressed to Radius Health, care of Paratek Pharmaceuticals. A Federal Register search for abaloparatide finds only a 2018 patent notice and no withdrawal.
| When | What happened |
|---|---|
| 1987 | Two reports describe a PTH-like protein from cancer. One purifies it from lung cancer cells, the other clones its gene. |
| Mar 2011 | The ACTIVE trial starts. It runs at 28 sites in 10 countries until October 2014. |
| Aug 2016 | ACTIVE is published in JAMA. |
| 28 Apr 2017 | FDA approves Tymlos for women past menopause at high fracture risk, carrying a boxed warning on bone cancer seen in rats. |
| 22 Dec 2021 | A label change takes the osteosarcoma boxed warning off. |
| 12 Dec 2022 | The EU authorises abaloparatide as Eladynos. |
| 19 Dec 2022 | FDA adds a use to raise bone density in men at high fracture risk. |
| 3 Aug 2026 | A label update brings in a warning on severe allergic reactions. |
An openFDA search finds no generic abaloparatide, only the Tymlos brand. In the EU it is Eladynos, held by Theramex. A listing is not proof that a product is on a given pharmacy shelf. Our medical review policy describes how approval facts get checked.
Sources: Drugs@FDA, NDA 208743 (Tymlos); FDA letter on the 2026 Tymlos allergy update; Federal Register search, abaloparatide; openFDA search for abaloparatide applications; EMA page for Eladynos; PTHrP gene cloned, Science 1987; PTHrP purified from lung cancer cells, PNAS 1987; ACTIVE trial, JAMA 2016; Tymlos launch label, April 2017; FDA letter adding the men indication, 2022
What else do people ask about Tymlos?
What is Tymlos?+
Tymlos is a US prescription drug for osteoporosis at high fracture risk. Its active part is abaloparatide, a lab-made chain of 34 amino acids. It is modeled on PTHrP, a cousin of parathyroid hormone. The FDA approved it on 28 April 2017 for women past menopause, and in December 2022 it added a use in men.
What is Tymlos used for?+
The US label lists two uses. One is treating osteoporosis in women past menopause who are at high risk of a fracture, where the label credits it with fewer spine and other fractures. The other is raising bone density in men with osteoporosis at high fracture risk. High risk means a past osteoporosis fracture, several risk factors, or other drugs that failed or could not be used.
Does Tymlos actually work?+
Against placebo, yes, in its main trial. In ACTIVE, 0.58% of women on abaloparatide had a new spine fracture over 18 months, against 4.22% on placebo. Breaks elsewhere in the body were 2.7% against 4.7%. Spine bone density rose 9.2% on Tymlos and 0.5% on placebo. Results for any one woman can differ from these averages.
Is Tymlos a bisphosphonate?+
No. Tymlos is a PTHrP analog. It switches on the PTH1 receptor and pushes bone-forming cells to make new bone. Bisphosphonates, such as alendronate, are a separate class of osteoporosis drug. In the ACTIVE extension, women who had finished Tymlos or placebo moved on to alendronate, so both classes appear in that one study.
What is abaloparatide?+
Abaloparatide is the drug inside Tymlos. The label calls it a synthetic peptide and an analog of PTHrP(1-34), the first 34 amino acids of that hormone. It matches PTHrP at 76% of those spots and PTH at 41%. One of its building blocks, Aib, is not one of the usual 20.
What is PTHrP?+
PTHrP stands for parathyroid hormone-related protein, also called PTH-related peptide. Scientists found it in 1987 while hunting the cause of high blood calcium in some cancers. Its gene clone made a protein of 141 amino acids that looks like PTH only at the start. Both hormones work through the same receptor on bone and kidney cells.
How is Tymlos related to Forteo?+
They are cousins, not the same drug. Both turn the same receptor, the PTH1 receptor, and both are US prescription drugs for osteoporosis. But Forteo is teriparatide, an exact copy of the start of PTH, grown in bacteria. Tymlos is abaloparatide, a built-from-scratch chain shaped after PTHrP that copies neither hormone exactly. Their labels also differ on uses and on the 2-year limit.
Does Tymlos prevent more fractures than Forteo?+
No study has shown that. The ACTIVE trial included both, but its main test was abaloparatide against placebo. A fair fracture race between the two would have needed about 22,000 women per group. Abaloparatide had less high blood calcium in ACTIVE, while more women on it stopped for side effects. Which drug fits one person is a question for that person and their doctor.
What are the side effects of Tymlos?+
In the women trial, the most common were extra calcium in the urine, dizziness, nausea, headache and a pounding heartbeat. Tiredness and upper belly pain were next. Men most often had skin redness or swelling where it goes in, dizziness and joint pain. The label also warns about allergic reactions, high blood calcium, kidney stones and a drop in blood pressure on standing.
What are the most serious risks of Tymlos?+
The label puts five warnings first. They are serious allergic reactions such as anaphylaxis, the rat bone cancer finding, low blood pressure on standing, high blood calcium, and extra urine calcium with kidney stones. Severe allergy to abaloparatide is the one firm reason never to use it. Most trial side effects were milder, like dizziness and nausea.
How long can you take Tymlos?+
The label says Tymlos has not been studied beyond 2 years, and it does not recommend more than 2 years over a lifetime. That is a label limit, not advice for one person. Forteo used to carry the same flat limit, but its label was changed in 2020 to allow longer use in some high-risk patients.
Does Tymlos cause osteosarcoma?+
In rats, yes: a 2-year study saw osteosarcoma, a bone cancer, rise with exposure, up to 87% of males at the top level. In people, nobody knows. The label says observational studies in humans have not shown a higher risk, though cases have been reported with drugs of this type. It still advises avoiding Tymlos in people with a higher baseline risk.
When was the Tymlos boxed warning removed?+
The 2017 launch label carried a boxed warning about the rat bone cancer. The December 2021 label lists that boxed warning as removed, and Drugs@FDA shows that change approved on 22 December 2021. Osteosarcoma is still one of the label warnings, just not in a box.
Can men take Tymlos?+
Since 19 December 2022 the US label includes men with osteoporosis at high fracture risk. That use is worded as raising bone density, not as preventing fractures. It rests on the ATOM trial of 228 men, where spine bone density rose 8.48% on abaloparatide and 1.17% on placebo over 12 months.
Is there a generic version of Tymlos?+
Not in the US as of 9 November 2026. An openFDA search for abaloparatide finds a single application, the Tymlos brand from Radius. Forteo is different: several teriparatide copies have been approved, as our Forteo page explains.
Is Tymlos approved in Europe?+
Yes, under another name. The European Medicines Agency lists abaloparatide as Eladynos, authorised across the EU on 12 December 2022. Its holder is Theramex Ireland Limited. The EMA overview describes use in women after menopause at increased risk of fracture.
Does Tymlos build bone?+
The label says it does. It switches on the PTH1 receptor, which starts the cAMP signal inside cells and pushes bone-building cells to lay down new bone. In rats and monkeys, bone mass and strength went up. In the women trial, spine bone density rose 9.2% on Tymlos against 0.5% on placebo over 18 months.
Sources: Tymlos prescribing information, revised August 2026; Drugs@FDA, NDA 208743 (Tymlos); ACTIVE trial, JAMA 2016; ATOM trial in men, JBMR 2022; PTHrP gene cloned, Science 1987; PTHrP purified from lung cancer cells, PNAS 1987; Tymlos label, December 2021 revision; openFDA search for abaloparatide applications; EMA page for Eladynos; Forteo prescribing information, revised August 2026
What did we learn about Tymlos?
Tymlos is abaloparatide, a built-from-scratch peptide shaped after PTHrP, a hormone first pulled from cancer cells in 1987. It turns the same bone receptor as Forteo, but cell tests suggest it favors a different receptor shape and gives shorter signals. In ACTIVE it cut spine fractures against placebo and caused less high calcium than teriparatide. More women stopped it for side effects, and no trial shows it prevents more fractures than Forteo.
Each Molecule Mechanics episode takes one medicine and animates what its label and trials report, and none of it is medical advice for anyone. The voice is an ElevenLabs AI narrator, and the animation is original. Earlier episodes covered tirzepatide, cagrilintide, the Wegovy pill and Foundayo.
Octreotide, prescribed in the US since 1988 for acromegaly and some hormone-making tumors, has its own octreotide article. One experimental peptide readers often look up is retatrutide, and our retatrutide calculator draws more Google visits than any other page here. Spotted an error? Our corrections policy says how to report it.
See every Molecule Mechanics episode
Sources: Molecule Mechanics on YouTube; Tymlos prescribing information, revised August 2026; ACTIVE trial, JAMA 2016
This page from Peptides Vietnam is for learning only and is not medical advice. It sums up what the Tymlos and Forteo labels, FDA files and published trials say. Any choice about a prescription drug is made by a patient together with the clinician caring for them.