Mesterolone is unique in that it is primarily formulated and used as an oral medication (e.g., under the brand name Proviron) and is not typically available or administered in injectable form. However, let’s address this in detail:

Oral Mesterolone Bioavailability

1. 1α-Methylation for Oral Use:

• Mesterolone is 1α-methylated, which allows it to resist rapid degradation during first-pass metabolism in the liver, making it orally bioavailable.
• Despite this modification, oral bioavailability is still relatively low compared to many C17-methylated steroids. Studies suggest its oral bioavailability is moderate and sufficient for therapeutic effects, though exact percentages are not widely documented (3% bioavailability).

1. Pharmacokinetics:

• Mesterolone is rapidly absorbed after oral administration, but it has a short half-life of about 12 hours, necessitating dosing multiple times a day (e.g., 25–50 mg, 1-3 times daily) to maintain stable levels.
• It is not extensively converted into estrogen or DHT metabolites due to its resistance to aromatase and 5α-reductase enzymes, which preserves its androgenic effects.

Injectable Mesterolone (Theoretical Bioavailability)

While injectable mesterolone is not commonly produced or studied, a comparison to other steroids provides some insight:

1. 100% Bioavailability: Injectable steroids bypass the liver during initial metabolism, meaning the active compound enters the bloodstream directly. This gives injectable steroids close to 100% bioavailability compared to oral forms.
2. Longer Half-Life:

• An injectable form of mesterolone could theoretically have a longer half-life, depending on whether an ester is attached. Esterified injectable steroids, such as testosterone enanthate or cypionate, are released gradually, extending the drug’s activity in the body.
• Without esterification, injectable mesterolone would likely have a similar duration of action to oral administration but would still avoid first-pass metabolism.

1. Potential Advantages of Injectable Mesterolone:

• Greater androgenic potency due to full bioavailability.
• Reduced frequency of administration compared to oral dosing.
• Elimination of potential liver strain, albeit minimal for oral mesterolone.

Practical Perspective

1. Why Injectable Mesterolone Is Rare:

• Mesterolone’s primary medical uses (e.g., treating infertility or boosting libido) do not demand the sustained levels achievable via injection.
• Its low anabolic activity makes it less desirable for injectable use in athletic or bodybuilding contexts compared to more potent injectable anabolic steroids.

1. Efficacy of Oral Mesterolone:

• Oral administration is sufficient for its intended androgenic effects, such as increasing free testosterone or enhancing libido.
• Even though its bioavailability is lower than injectables, the therapeutic doses (25–75 mg daily) are effective and well-tolerated.

Summary

If you’re considering a practical use case, oral mesterolone is the standard. Injectable versions would theoretically be more bioavailable but are impractical due to the compound’s specific androgenic niche. Let me know if you’d like to explore further details!