# Primobolan (Injectable)

*Also known as: Methenolone Enanthate, Primo*

Injectable methenolone enanthate; very long half-life, mild profile. Peak calibrated.

## Overview

Primobolan injectable (methenolone enanthate) is a DHT-derived injectable carrying the C17beta enanthate ester, originally introduced clinically for wasting conditions and valued for a very mild side-effect profile relative to other injectables. It binds the androgen receptor, does not aromatize, and is already a DHT derivative so it is not further 5-alpha-reduced. Its 10.5-day half-life supports a twice-weekly injection schedule in research protocols, with a long run-up to steady state. Hepatotoxicity is rated none (injectable route avoids the 17-alpha-methyl first-pass burden seen with the oral form), which is a core reason it is perceived as clean. The trade-off is that the mild profile means results are slow and modest. HPTA suppression occurs but is comparatively gentle at moderate doses.

## Pharmacokinetics

- **Model tier:** simple
- **Half-life:** 10.5 days (252 hours)
- **Cmax:** 88.9 ng/dL
- **Bioavailability:** 73%

## Dosing

- **Default dose:** 200 mg
- **Typical range:** 200–400 mg
- **Units:** ng/dL

## Harm reduction

- **Aromatizes:** No
- **DHT derivative:** Yes
- **Injection frequency:** 2×/week

## Detection time (anti-doping)

- **Window:** 21–40 days post-last-dose
- **Target metabolite:** Methenolone sulfate metabolites
- **Assay:** LC-MS/MS
- **Notes:** Sulfated conjugates are the long-lived markers (~17 days via sulfate; earlier studies ~40 days for parent metabolites).

## Source

- **Label:** Llewellyn reference
- **URL:** https://books.google.co.uk/books?id=w4ZUJAdleTsC
- **Notes:** Cmax calibrated to ng/dL serum peak.

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