Clinical-stage

Steady thyroid hormone, once a day

Thyropeutics is a clinical-stage company developing PZL, an investigational T3 designed to be taken once a day alongside standard thyroid therapy.

PZL is an investigational drug. The FDA has not approved it. Its safety and effectiveness have not been established, and it is not available for sale or prescription.

Our mission

We’re on a mission to provide a better thyroid medication to the over 20 million Americans who depend on one daily.

20 million: Americans on thyroid hormone replacement, ClinCalc DrugStats, 2024. Images are illustrative; people shown are models.

The problem

Today’s medications fall short.

Over 20M Americans take thyroid medication, mostly T4, the second most prescribed drug in the US.

T4 alone falls short.

4.5M+

More than 1 in 4 still have symptoms on today’s leading medication (T4 Synthroid)

Up to

45%

higher mortality risk than patients also taking T3

Up to

37%

higher dementia risk than patients also taking T3

Associated with T4 alone in a 20-year observational study of 1.26 million patients.

Today’s T3 is too risky.

Taking T3 with T4 can help, but its instant-release can cause discomfort (palpitations, tremors etc.), require repeated dosing, and introduce compliance issues.

Sources: ClinCalc DrugStats, 2024 (levothyroxine #2 by prescriptions). One in four: Hidalgo et al., Endocr Pract, 2023 (26.7 to 28%); 4.5M is about one in four of 18.3M on T4 alone (company model). Risk: Beltrão et al., J Clin Endocrinol Metab, 2025, Table 6, T4 monotherapy vs combination therapy; observational; the senior author is a consultant to the company. T3: Cytomel prescribing information.

The American, British and European Thyroid Associations have clearly and unanimously stated the need for extended-release T3.

Source: Jonklaas et al., Thyroid 2021;31(2):156-182 (ATA/BTA/ETA consensus, Statement 6.3, 100% agreement).

Meet PZL

Meet PZL, an extended-release T3

PZL is the first extended-release T3 medication in clinical trials, with the potential to improve millions of lives and meet a major unmet need.

30%

lower peak T3 than today’s T3

6 h

Plateau duration

12 h

T3 still above half of its peak

01

Protected through 2039

02

Composition-of-matter patent, granted in the US, Europe, UK, Japan and India

03

No extended-release T3 on the market or in any reported clinical trials

Chemical structure of PZL: T3 molecules linked through zinc atoms in a repeating chain — PZL: poly-zinc-liothyronine, a polymeric coordination complex of zinc and T3

Zinc links T3 molecules into a chain that adheres to the gut lining. T3 is designed to release gradually and avoid the spike of today’s T3.

Chart: Phase 1, double-blind, randomized, placebo-controlled crossover at the University of Chicago, funded by the NIH; 12 healthy volunteers enrolled, 9 analysed; single 50 mcg dose; redrawn from Table 2 (mean serum T3). One small study of single doses in healthy volunteers; it did not test patients and does not establish that PZL is safe or effective. Dumitrescu et al., Thyroid, 2021, doi:10.1089/thy.2021.0304. Patent: company patent records (US patent issued August 2023; expiry 2039). Mechanism: company; Dumitrescu et al. 2021. PZL is investigational.

The opportunity

Millions are in need of a better medication, both in the US and globally

1.8M+people currently taking a T3 medication who need lower-risk, more-effective T3

4.5M+symptomatic T4 users who are too unhealthy to risk taking instant-release T3

13M+remaining patients on T4 who have low T3 and higher mortality and dementia rates

18.6M+on thyroid hormone replacement in the EU, UK and Japan

US: ClinCalc DrugStats 2024 (20.1M on thyroid hormone replacement, incl. 1.8M on T3-containing medication); 4.5M is 25% of 18.3M on levothyroxine with residual symptoms (company model, August 2026; Hidalgo et al. 2023 found 26.7%). EU: Eurostat 2025 x 3.6% (CoLaus, PLOS One 2021). UK: England hypothyroidism register, 2022. Japan: Japan Thyroid Association, citing MHLW Patient Survey 2023. Images are illustrative; people shown are models.

The team