Testosterone Undecanoate

Ester: Undecanoate -- 11-carbon chain ester dissolved in castor oil. Ultra-slow release providing stable testosterone levels over 10-14 weeks from a single injection.

Dosage:

• TRT: 1000 mg (4 mL) every 10-14 weeks after an initial loading phase (second injection at 6 weeks)
• Not typically used for enhancement due to the extremely long half-life and slow dose adjustment

Injection Protocol:

• Deep IM injection only (gluteal), 21-23g needle, 1.5-2 inch
• Must be injected very slowly (over 2 minutes minimum) due to the 4 mL oil volume
• Administered in-clinic in many countries due to rare pulmonary oil microembolism (POME) risk
• Not suitable for SubQ injection

Key Notes:

• Preferred TRT option in Australia, UK, and Europe (Nebido); available in the US as Aveed
• Eliminates the need for weekly injections, improving adherence
• Slower dose titration: takes 2-3 injections (20-30 weeks) to reach steady state
• Bloodwork timing is different from short esters: test at the midpoint or trough (week 8-10) of the injection interval
• Aromatisation is typically lower and more stable than with shorter esters due to the flat release curve
• Not practical for PCT transitions due to the extremely long clearance time (3-4 months)

How Nebido compares to the weekly esters on half-life, dosing and level stability: Testosterone esters compared.