Carrier Oils
Most above board compounding pharmacies use castor, sesame, cottonseed, or sunflower oil for making HRT.
Most DIY homebrewers are using medium chain triglyceride (MCT) oil. Sometimes called “Viscoleo,” MCT oil is more viscous and therefore may make the absorption rate quicker. It’s viscousness makes it easier to inject for the clients and easier to filter for the brewers.
MCT oil is a mix of C8 and C10 fatty acids. Your bottle of MCT should tell you the ratio of these two, I’ve found that most pharmaceutical grade MCT is a 60/40 blend of C8/C10. If you’d like to calculate the oil density you should know the blend ratio.
Some more info from an article on Transfeminine Science below:
It is in any case known from other studies that different oil vehicles are absorbed at different rates from the injection site and can result in different concentration–time curve shapes. This is thought to be due to differences in oil lipophilicity and depot release rates. Viscosity of oils has also been hypothesized to potentially influence rate of depot escape. However, research so far has not supported this hypothesis. Oil vehicles can vary with injectable estradiol preparations even for the same estradiol ester. For instance, pharmaceutical estradiol valerate is formulated in sesame oil , castor oil , or sunflower oil depending on the preparation (Table ). It is notable however that these three oils have similar lipophilicities (Table ). On the other hand, homebrewed injectable estradiol preparations used by DIY transfeminine people often employ medium-chain triglyceride (MCT) oil as the oil vehicle. This oil (in the proprietary form of Viscoleo) has notably been found to be much more rapidly absorbed than conventional oils like sesame oil and castor oil in animals. In addition, although based on very limited data, MCT oil has been found to give spikier and shorter-lasting depot injectable curves in humans. As such, injectable estradiol preparations using MCT oil as the vehicle may have differing and less favorable concentration–time curve shapes than pharmaceutical injectable estradiol products. Other excipients, like benzyl alcohol , as well as factors like injection site and volume, have additionally been found to influence pharmacokinetic properties with depot injectables. Excipients besides oil vehicle also vary by formulation (Table ).