Cognitive & neuro
Protirelin (TRH)
Synthetic thyrotropin-releasing hormone: an approved diagnostic injection whose brain-related uses failed in trials.
What it is
Protirelin is synthetic thyrotropin-releasing hormone, a three-amino-acid peptide (pyroglutamyl-histidyl-prolinamide). It is an approved medicine as a diagnostic injection for testing thyroid and pituitary function, and it was studied for decades as a treatment for depression, motor neurone disease and cognitive impairment without producing a durable benefit.
How it works
- 1
Binds TRH receptors on the anterior pituitary, releasing thyroid-stimulating hormone.
- 2
Acts as a neuromodulator in the brain, influencing acetylcholine, dopamine and glutamate signalling.
- 3
Is broken down within minutes, which limits any sustained central effect.
- 4
Analogues were developed to resist that breakdown and cross into the brain better.
- 5
Raises prolactin in some situations, which is used diagnostically.
What it's studied for
Reported and studied effects
- A rapid, measurable TSH rise in the diagnostic test
- Antidepressant and motor neurone trials showed inconsistent or transient effects
- Any cognitive benefit was not sustained in controlled studies
Research protocol notes
Research context onlyResearch context only - an approved diagnostic and an unsuccessful therapeutic. The diagnostic test uses 200 to 500 micrograms intravenously with TSH sampled at 20 to 30 minutes. Neuropsychiatric trials used repeated injections or infusions over days to weeks and did not produce durable benefit.
These figures are described so you can understand what researchers did. They are not a dose, a schedule, or a suggestion — and they are not a substitute for a doctor.
Possible side effects and contraindications
Safety profile
Possible side effects
- Nausea
- Flushing and a warm sensation
- Urgent need to urinate
- Dizziness
- Transient changes in blood pressure and heart rate
- Rare arrhythmia
Contraindications and cautions
- Prior hypersensitivity
- Untreated adrenal insufficiency
- Cardiac disease needs caution
- Pregnancy only if clearly needed
A side-effect list is never complete, and these are not the only situations that warrant caution. Anything unexpected, or anything you are unsure about, should be discussed with a doctor before use.
Evidence assessment
The diagnostic use is well established, but the cognitive and psychiatric claims come from mostly small, negative or inconsistent trials from the 1970s to 1990s.
References
References link to published literature, regulator pages or literature indexes. Where a link points to a search, it collects the peer-reviewed work on that molecule rather than a single study.
Related
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The nerve-acting fragment of ACTH, developed as a drug candidate for nerve damage and cognitive decline, and abandoned.
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BDNF (brain-derived neurotrophic factor)
The brain's main growth factor for plasticity: essential, widely measured, and not something a supplement can deliver.
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Cerebrolysin
A porcine brain peptide mixture licensed in parts of Eastern Europe and Asia for stroke and dementia, without EMA or FDA approval.