Testosterone Decanoate: This is a testosterone ester with a 10-carbon decanoate chain attached to the testosterone molecule. It is typically used in injectable forms and has a longer duration of action compared to some other testosterone esters, meaning it stays in the body for a longer period before needing another injection.

Testosterone Undecanoate: This is another testosterone ester, but it has a longer 11-carbon undecanoate chain attached to the testosterone molecule. Testosterone undecanoate is commonly used in oral formulations, such as capsules or tablets. It has a unique pharmacokinetic profile, providing a slow and sustained release of testosterone in the body over several weeks. This makes it suitable for testosterone replacement therapy with less frequent dosing.