Tabimorelin

Tabimorelin was developed alongside ipamorelin at Novo Nordisk as the orally bioavailable member of the programme, agonising GHS-R1a at the somatotroph and hypothalamus to raise pulsatile GH and, with chronic dosing, IGF-1. Phase 1 and 2 work in healthy adults and in GH-deficient patients confirmed a dose-dependent GH rise, and doses of around 0.5 to 1 mg/kg daily raised IGF-1 meaningfully over weeks. Development stopped because tabimorelin proved to be a potent CYP3A4 inhibitor - creating an unacceptable drug-interaction burden - and because chronic dosing raised liver transaminases. It is essentially never available on the grey market, and its main value now is as a cautionary illustration that oral secretagogues are chemically hard to get right.

Targets: GHS-R1a (ghrelin receptor), Pituitary somatotrophs, CYP3A4 (off-target inhibition)

• · Trials used weight-based oral doses in the region of 0.5 to 1 mg/kg daily - roughly 35 to 80 mg for an adult. There is no established consumer protocol and the compound is not meaningfully available.

Work out your exact syringe units →

• very commonDrug interactions from CYP3A4 inhibition— Not a side effect in the usual sense, but the practical reason it was shelved.
• commonElevated liver transaminases— The finding that ended development on chronic dosing.
• commonIncreased appetite— Class effect for GHS-R1a agonists.
• commonIncreased sweating— Reported in the early human studies.
• uncommonFatigue
• uncommonReduced insulin sensitivity

• Any existing liver disease or elevated transaminases.
• Concomitant use of CYP3A4 substrates with a narrow therapeutic index.
• Active malignancy.
• Pregnancy and breastfeeding.

• conflictCYP3A4 substrates — Tabimorelin inhibits CYP3A4, raising levels of a very large number of common medications. This is its defining pharmacological problem.
• redundantmk-677 — Same target, and MK-677 has far more human data without the CYP3A4 issue.
• conflictStatins — CYP3A4-metabolised statins would accumulate, raising myopathy risk.

• · Liver function tests would be mandatory with any use, given the documented transaminase signal.
• · IGF-1.
• · Fasting glucose.

Never approved anywhere and not commercially available. Would fall under WADA S2 as a GH secretagogue.

• Zdravkovic et al., phase 1 pharmacokinetics and pharmacodynamics of the oral secretagogue NN703 in healthy adults (trial)
• Novo Nordisk discontinuation of tabimorelin over CYP3A4 inhibition and hepatic enzyme elevation (other)

Tabimorelin's value now is entirely as a cautionary case, and it is a good one. Novo Nordisk developed it alongside ipamorelin as the orally bioavailable member of the same programme, and the pharmacology worked: Zdravkovic's single-dose study in healthy male volunteers and Agersø's PK/PD modelling both confirmed oral activity and a dose-dependent GH response, and Svensson's study in adult patients with growth hormone deficiency confirmed the effect in the target population with chronic dosing raising IGF-1 meaningfully over weeks. What killed it was off-target chemistry. Tabimorelin proved to be a potent CYP3A4 inhibitor, and CYP3A4 handles a very large fraction of all prescription drugs - statins, many benzodiazepines, calcium channel blockers, immunosuppressants, several anticoagulants. A drug that inhibits it creates an interaction burden that no wellness indication can justify. Chronic dosing also raised liver transaminases. Both problems are structural rather than dose-scheduling problems, and both are the reason the compound does not exist commercially. The general lesson is worth carrying: getting a small molecule to hit GHS-R1a orally is not the hard part - MK-677, anamorelin and macimorelin all manage it - the hard part is doing so without hitting something else. Tabimorelin hit CYP3A4. MK-677 hits glucose metabolism. Anamorelin hits glucose and cardiac conduction. There is a pattern here.

Nothing goes wrong in practice because the compound is essentially unobtainable, and that is the correct outcome. If it were available, the two failure modes are the ones that ended its development: unpredictable interactions with anything metabolised by CYP3A4, and liver enzyme elevation on chronic dosing. Neither is manageable with dose adjustment. The reason it is worth a record at all is historical and educational - it is the clearest demonstration that oral GHS-R1a agonism is chemically achievable and pharmacologically clean at the receptor, and that the problems come from everything else the molecule touches.

• GHS-R1a (ghrelin receptor), pituitary somatotroph — Orally active agonist; no quantitative affinity resolved

  Dose-dependent acute GH release and, with chronic daily dosing, meaningful IGF-1 elevation over one to two weeks.

• CYP3A4 — Potent inhibitor

  The defining problem with the molecule. Raises plasma levels of a very large number of common medications. This is why development stopped, not a footnote to it.

• Hepatocytes — Not applicable

  Elevated transaminases on chronic dosing - the second reason development stopped.

• Arcuate NPY/AgRP neurons — Not characterised

  Increased appetite, a class effect for GHS-R1a agonists, reported in the early human studies.

• Zdravkovic et al., single-dose pharmacokinetics, pharmacodynamics, safety and tolerability of NN703 in healthy male volunteers 1 · 2000

  Established oral activity, safety and tolerability of a single dose, with a measurable GH response. The first human study of the compound.

• Agersø et al., pharmacokinetic and pharmacodynamic modelling of NN703 after a single oral dose in human volunteers 1 · 2001

  Quantitative PK/PD modelling of the oral dose to GH response relationship.

• Svensson et al., oral NN703 in adult patients with growth hormone deficiency 2 · 2003

  GH and IGF-1 response to chronic oral administration in the target patient population - the study that took the compound from proof of concept into a real indication before development stopped.

GH rises acutely after a single oral dose; IGF-1 climbs over one to two weeks of daily dosing. Transaminase elevation, where it occurred, was a chronic-dosing finding - which means the trials long enough to show benefit were the same trials that showed the liver signal.

The only stacking conversation worth having about tabimorelin is a negative one, and it is not about other secretagogues - it is about the entire contents of a medicine cabinet. A potent CYP3A4 inhibitor raises the plasma levels of a very large number of common drugs, and the consequences range from a mildly stronger benzodiazepine to statin-induced rhabdomyolysis. Anyone taking a CYP3A4-metabolised statin, a calcium channel blocker, an immunosuppressant or a direct oral anticoagulant should not go near this. Other GHS-R1a agonists are redundant, and MK-677 does the same job with far more human data and without the CYP problem.

Against MK-677: MK-677 is the same idea done successfully - orally active GHS-R1a agonism with vastly more human data and no CYP3A4 problem. There is no scenario in which tabimorelin is preferable. Against ipamorelin: developed in the same Novo Nordisk programme, and the contrast is instructive. Ipamorelin survived as a research chemical because it is clean at the receptor and inert everywhere else; tabimorelin died because oral bioavailability came bundled with off-target chemistry. Against anamorelin and macimorelin: both are orally active GHS-R1a agonists that made it to approval somewhere, which shows the problem was tabimorelin specifically rather than the concept.

Not commercially available in any form and not meaningfully present on the grey market. There is no price because there is no supply.

• ?No half-life, tmax, bioavailability, clearance or volume of distribution values were extracted from the primary publications in this session, despite those publications existing.
• ?No molecular weight or structural formula was resolved.
• ?The magnitude and reversibility of the transaminase elevation are not characterised in the sources reached here.
• ?The specific reasons Novo Nordisk gave for discontinuation are widely reported as CYP3A4 inhibition and hepatic enzyme elevation but were not verified against a primary company or regulatory document.
• ?The 0.5 to 1 mg/kg daily trial dose range quoted in the Core record was not confirmed from the primary publications.
• ?There is no modern safety follow-up of anyone who took this compound.

• The pharmacokinetics, pharmacodynamics, safety and tolerability of a single dose of NN703, a novel orally active growth hormone secretagogue in healthy male volunteers Zdravkovic M, Søgaard B, Ynddal L, Christiansen T, Agersø H, Thomsen MS, Falch JE, Ilondo MM, Growth Hormone and IGF Research, 2000 · PMID 11032702

  The first-in-human study.

• Pharmacokinetic and pharmacodynamic modeling of NN703, a growth hormone secretagogue, after a single po dose to human volunteers Agersø H, Ynddal L, Søgaard B, Zdravkovic M, Journal of Clinical Pharmacology, 2001 · PMID 11210396

  The quantitative human PK/PD characterisation, and the only real pharmacokinetic source for this compound.

• Oral administration of the growth hormone secretagogue NN703 in adult patients with growth hormone deficiency Svensson J, Monson JP, Vetter T, Hansen TK, Savine R, Kann P, Bex M, Reincke M, Hagen C, Beckers A, Ilondo MM, Zdravkovic M, Bengtsson BA, Korbonits M; NN703 Clinical Research Group, Clinical Endocrinology (Oxford), 2003 · PMID 12699438

  The phase 2 study in the target population, and the last substantial publication before development ended.