TRH (Protirelin) and Taltirelin

Sexual health, hormones & signalling

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Note on this profile. Protirelin is an approved diagnostic (and in Japan therapeutic) medicine in some countries and discontinued in others; taltirelin is approved only in Japan. Neither is a research-only compound in the usual sense, but protirelin has a small research-community following. This page explains the published science.

Summary

Class: TRH: naturally occurring hypothalamic tripeptide (pyroglutamyl-histidyl-prolinamide); protirelin is the synthetic copy. Taltirelin: synthetic TRH analogue with a modified N-terminal residue, orally active and longer lasting
Mechanism: TRH tells the pituitary to release TSH (and prolactin); in the brain it acts as a neuromodulator that increases arousal, motor activity and cerebellar output — taltirelin was built to exploit the brain effects with minimal thyroid effect
Routes studied: TRH: intravenous (diagnostic), intramuscular (Japan), intrathecal and intranasal (research), oral (poorly absorbed). Taltirelin: oral
Dose range reported: TRH test: 200–500 µg IV (commonly 200 µg adults, 7 µg/kg children) with TSH sampled at 0, 20–30 and 60 minutes. Hirtonin (Japan, spinocerebellar degeneration): 0.5–2 mg IM/IV daily for 2-week courses. Taltirelin label (Japan): 5 mg orally twice daily. ALS trials: up to 500 mg/day IV or intrathecal. Community-reported: occasional intranasal or subcutaneous use in the 0.1–1 mg range for mood or "longevity", resting on rodent data — anecdotal
Half-life: TRH: ~5 minutes in plasma (rapidly cleaved by pyroglutamyl peptidase); TSH peak at 20–30 minutes. Taltirelin: oral bioavailability modest; plasma half-life ~1–2 hours with CNS action lasting much longer than TRH †
Storage: Lyophilised: refrigerate. Reconstituted protirelin: refrigerate, use within days (community practice); solutions for injection per label
Regulatory status: Protirelin approved as a diagnostic in some EU countries and Japan; discontinued in the US. Taltirelin approved only in Japan

Doses are as reported in studies or by the community — never recommendations.

1What it is

TRH is the smallest of the classical hypothalamic hormones — just three amino acids — and the first to have its structure solved, in 1969, work that contributed to the 1977 Nobel Prize (Guillemin and Schally). It is released into the pituitary portal blood and triggers TSH, which drives the thyroid. Synthetic TRH (protirelin) became the "TRH stimulation test" of the 1970s–1990s: an injection followed by TSH measurements to probe pituitary thyrotroph function and to separate hypothalamic from pituitary causes of low thyroid function. Highly sensitive TSH assays have made the test largely obsolete, and the US product (Thyrel TRH) was discontinued around 2002; it remains available in Germany (Relefact TRH) and a few other countries.

Separately, TRH is widely distributed in the brain and spinal cord, where it acts as a neurotransmitter-like signal independent of the thyroid. That led Japan to approve injectable TRH (Hirtonin) in the 1980s for the ataxia of spinocerebellar degeneration, and then to develop taltirelin (Ceredist, approved 2000), an oral analogue roughly 10–100-fold more potent in the brain and longer acting, with far weaker TSH release. Taltirelin has never been approved outside Japan. Trials of TRH in ALS, depression and brain injury in the West were largely negative or inconclusive.

A small research-community interest in TRH exists, mostly stemming from a 2013 paper reporting that TRH in drinking water prolonged life and improved kidney and testicular histology in ageing mice; human evidence for any such use is absent.

2How it's thought to work

Pituitary. TRH binds TRH-R1 on thyrotrophs (TSH release) and lactotrophs (prolactin release), via Gq/phospholipase C and calcium signalling.

Brain. TRH receptors are dense in the cerebellum, brainstem, spinal cord motor neurons, hippocampus and limbic regions. TRH increases release of acetylcholine, noradrenaline and dopamine, enhances motor neuron excitability, counteracts sedation from alcohol and barbiturates, and has anticonvulsant and arousal-promoting effects in animals. In cerebellar ataxia the proposed mechanism is enhanced cerebellar and brainstem motor output, though the precise target is unclear.

Taltirelin. is more resistant to pyroglutamyl peptidase, penetrates the brain and achieves sustained receptor activation; in rodents it increases dopamine turnover and locomotor activity for hours.

TRH from the hypothalamus reaching the anterior pituitary, which releases TSH; TSH drives the thyroid to make T4 and T3. The thyroid hormones then feed back on the pituitary and hypothalamus to ease the signal off.Schematic — not to scale

3What the research shows

Graded A (diagnostic accuracy, historical)

TRH stimulation test

Decades of use established the normal TSH rise (roughly 5–30 mIU/L above at 20–30 minutes), the blunted response of hyperthyroidism and pituitary disease, and the exaggerated/delayed response of hypothalamic disease (reviewed in Faglia 1998, Thyroid †). The test is still used in a few niche situations (central hypothyroidism in children, TSH-secreting adenomas, resistance to thyroid hormone) and in rodent neuroendocrine research.

Graded A (small Japanese trials)

Spinocerebellar degeneration

Double-blind trials of IM TRH in Japan in the 1980s reported modest improvement in ataxia scores (Sobue 1983, Lancet — letter/short report †). Taltirelin's approval rested on Japanese randomised, double-blind trials showing improvement in ataxia rating scales versus placebo over 4–24 weeks (reported in Japanese regulatory documents and in Kinoshita 1998, Arzneimittelforschung †). Effect sizes were modest and outcome measures were clinician-rated; independent non-Japanese replication is essentially absent. Spinocerebellar ataxia guidelines outside Japan do not recommend TRH analogues. [3]

Graded A (negative)

Amyotrophic lateral sclerosis

Following dramatic single-case reports in the early 1980s, controlled trials of high-dose IV and intrathecal TRH found transient improvements in strength lasting hours but no durable benefit (Brooke 1986, Neurology †; Mitsumoto 1986, Neurology). Taltirelin was also tested in a small Japanese ALS study without convincing benefit. [5]

Depression

Blunted TSH response to TRH was one of the most studied biological markers in 1970s–1980s psychiatry; intrathecal and intravenous TRH produced short-lived mood improvement in small open studies of refractory depression (Marangell 1997, Arch Gen Psychiatry — intrathecal, n=8). No approved use. [4]

Graded C/D

Other

Rodent data on seizure suppression, spinal-cord injury recovery, arousal from anaesthesia, and the 2013 lifespan study (Pierpaoli 2013, Rejuvenation Res — mice given TRH in water showed improved survival and organ histology). None has human confirmation. [2]

4Reported side effects and interactions

Literature-reported

Literature (TRH test). a brief but striking cluster within a minute of injection — urge to urinate, nausea, flushing, metallic taste, light-headedness, headache, tight chest, transient blood pressure rise or fall; rarely bronchospasm or seizure; isolated reports of pituitary apoplexy in people with large adenomas. Transient prolactin rise. Taltirelin (Japanese label): nausea, headache, dizziness, palpitations, drowsiness or insomnia, raised prolactin, mild TSH/thyroid hormone changes, elevated liver enzymes; hypersensitivity rarely.

Community-reported

anecdotal reports of nausea, flushing and jitteriness with intranasal or injected TRH; some report mood or energy lift lasting hours.

Theoretical. repeated TRH could raise prolactin and disturb thyroid feedback; arousal effects could worsen anxiety or insomnia; unknown long-term effects on thyrotroph function.

Interactions. levothyroxine, glucocorticoids, dopamine , somatostatin and antithyroid drugs all alter the TSH response and confound the test; taltirelin may enhance effects of other dopaminergic or stimulant drugs (mechanistic inference).

Markers researchers commonly monitor

Based on the hormone's physiology and the diagnostic protocol:

Marker	Why it's watched
TSH, free T4, free T3	TRH drives TSH; repeated dosing could shift thyroid function; baseline and follow-up are the obvious markers.
Prolactin	rises acutely with TRH; a sustained rise with repeated use would matter.
Blood pressure and heart rate	transient changes are the main acute effects.
Ataxia rating scales (SARA or ICARS), gait video	the outcome in the Japanese indication; subjective impressions are unreliable.
Liver enzymes	listed for taltirelin.
Sleep and anxiety self-rating	arousal effects are the most plausible subjective change.

Free for everyone. Safety information is never behind a paywall.

5Reconstitution and handling

Protirelin for the diagnostic test is supplied as 200 µg or 500 µg ampoules or vials for IV injection. Research-grade TRH is with ; the compound is small and hydrophilic, dissolves readily, and degrades in solution over days to weeks. Taltirelin is an oral tablet (5 mg) with no reconstitution. (protirelin only)

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6Commonly studied alongside

Levothyroxine and liothyronine (thyroid axis), GnRH and CRH tests in combined pituitary function testing (see Corticorelin, #218; gonadorelin in #102–#108), riluzole (ALS comparator era), other ataxia candidates (riluzole, troriluzole, acetyl-DL-leucine), and in the community, semax/selank-type nootropic peptides without any combined study.

Informational cross-links. Not stack recommendations.

7Regulatory status by region

Region	Status (checked —)
United States	Protirelin (Thyrel TRH) FDA-approved as a diagnostic but discontinued (~2002); no marketed product. Taltirelin not approved
European Union	Protirelin nationally authorised as a diagnostic in some states (e.g. Germany, Relefact TRH) †; taltirelin not authorised
United Kingdom	Protirelin not currently licensed; available only as an unlicensed import †; taltirelin not licensed
Australia	Protirelin not registered on the ARTG †; taltirelin not registered
South Africa	Not registered †
Sport (WADA)	Not named on the Prohibited List; TRH and analogues are not listed under S2 as of the current list †

8Open questions

Does taltirelin's benefit in spinocerebellar degeneration hold up in independent, modern, placebo-controlled trials outside Japan?
Whether TRH or analogues have any role in depression or disorders of arousal (research into TRH-based compounds for narcolepsy continues at the preclinical stage).
The mouse longevity finding has no replication; human relevance is entirely unknown.

9References

1Burgus R et al. (1969). Structure moléculaire du facteur hypothalamique hypophysiotrope TRF d'origine ovine. C R Acad Sci Hebd Seances Acad Sci D. [verify] PubMed
2Pierpaoli W (2013). Aging-reversing properties of thyrotropin-releasing hormone. Curr Aging Sci. [verify journal] PubMed · DOI
3Kinoshita K et al. (1998). Taltirelin hydrate (TA-0910): an orally active thyrotropin-releasing hormone mimetic agent with multiple actions. CNS Drug Rev. [verify] DOI
4Marangell LB et al. (1997). Effects of intrathecal thyrotropin-releasing hormone (protirelin) in refractory depressed patients. Arch Gen Psychiatry. PubMed · DOI
5Mitsumoto H et al. (1986). Thyrotropin-releasing hormone in amyotrophic lateral sclerosis: a controlled trial. Neurology. [verify] PubMed
6Gary KA, Sevarino KA, Yarbrough GG, Prange AJ, Winokur A (2003). The thyrotropin-releasing hormone (TRH) hypothesis of homeostatic regulation: implications for TRH-based therapeutics. J Pharmacol Exp Ther. PubMed · DOI
7Ceredist (taltirelin hydrate) Japanese package insert (current). PubMed

References are being resolved to PubMed/DOI identifiers; links search PubMed for the citation until then.

† Being confirmed by our reviewers against current sources.

10Community

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11Page history

31 Oct 2026Profile published — awaiting medical review

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