# Testosterone Undecanoate (Castor Oil)

*Also known as: Nebido, TU, Reandron*

Very long-acting ester (Nebido). Dosed 1000 mg every 10–14 weeks for TRT. NHS standard.

## Overview

Testosterone undecanoate in castor oil (brand Nebido, Reandron) is the longest-acting testosterone ester, formulated for deep intramuscular depot injection. The 11-carbon undecanoate chain and the viscous castor-oil carrier slow hydrolysis so the ester releases testosterone gradually over months. The dataset records a half-life of 33.9 days (about 814 hours), with Cmax near 800 ng/dL and a Tmax of roughly 10 days at the clinical 1000 mg dose. Clinical protocols dose it at 1000 mg every 10 to 14 weeks, which keeps most men in range with only 4 to 5 injections per year. It aromatizes to estradiol and is not hepatotoxic. The trade-off for that convenience is slow onset and limited dose-tuning flexibility, so it suits stable maintenance TRT rather than rapid titration.

## Pharmacokinetics

- **Model tier:** advanced
- **Half-life:** 33.9 days (813.5999999999999 hours)
- **Cmax:** 800 ng/dL
- **Tmax:** 10.0 days
- **Bioavailability:** 65%

## Dosing

- **Default dose:** 1000 mg
- **Typical range:** 750–1000 mg
- **Units:** ng/dL

## Harm reduction

- **Aromatizes:** Yes
- **DHT derivative:** No
- **Injection frequency:** Every 10–14 weeks

## Source

- **Label:** Bayer Nebido Prescribing Information
- **URL:** https://www.bayer.com/sites/default/files/NEBIDO_EN_PI.pdf
- **Notes:** Cmax calibrated to ng/dL serum peak (Nebido 1000mg → ~600–900 ng/dL).

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**Canonical URL:** https://anabolicdex.com/compounds/testosterone-undecanoate-castor
**Plot:** https://anabolicdex.com/plot?compound=testosterone-undecanoate-castor