Having found that I have a lowish SHBG (22; normal range 16.5-55.9), and having what I believe to be related clincal symptoms, I've decided to follow the advice of some members of this forum, and increase the frequency of my injections from 2x/wk to daily injections. What I'm now trying to decide is whether I should go with shallow IM vs. SC. I'd prefer SC, but it seems like some guys (not all) have issues with SC resulting in lower T levels and higher estrogen levels. (The estrogen issue is very important to me as I am prone to gynecomastia, and I'd like to avoid an AI if possible.)
I've also been scouring the literature for guidance. I came across a study (Sex Med 201;3:269-279) in which one group of patients was given 100mg testosterone enanthate subq 1x/week, and another group was given 200mg testosterone enanthate IM 1x/week. At steady state, the subq group had a mean T of 896 ng/dL, while the IM group had a mean T of 1659 ng/dL. This is not surprising, given that the IM group was getting twice as much T. The interesting thing, however, is what happened to their estrogen levels. Despite the greatly different T levels, both groups had the same mean E2 level of about 50 pg/mL. In other words, the IM group had a T:E ratio almost double the SC group! Now granted, they were doing weekly injections not daily, but clearly there was some extra conversion to estrogen with the subq group. I assumed this was due to aromatase in the subq tissues.
But the explanation is not that simple. As pointed out by Dr. Saya in another thread, we are not injecting testosterone, but rather we are injecting T esters, and T esters should not be affected by aromatase. Now, I suppose if you inject a big blob of oil (as with weekly SC injections), there might be some local conversion of the esterified T into active T, and then subsequent conversion into estrogen. However, with smaller blobs of oil (as with daily SC injections) I imagined systemic absorption should be rapid enough that there is insufficient time for any local conversion--the esterified T should safely make it into the systemic circulation, where aromatase becomes less of an issue. This line of reasoning would explain both the study I mentioned above, where they used big weekly injections, as well as the experience of some on this forum, where small daily injections made no difference.
Well, anyway, that was my thinking. However, as I continued to look into the research, I realized the picture in my mind was incorrect, or at least incomplete. What I had originally pictured in my mind is that the blob of oil we inject into our bodies, whether IM or SC, is absorbed systemically fairly rapidly. I pictured microscopic droplets of oil being distributed thoughout the body in a matter of minutes or hours. I then imagined the esterified T within these tiny droplets being very gradually converted into active form (by the esterase enzyme--which is ubiquitous in the body). This conversion takes place over a matter of days, leading to the long half lives of T esters (e.g. 8 days for testosterone cypionate).
So this is how I pictured things happening. But I was wrong. This is not what happens. As I said earlier, esterase is everywhere in the body. This means that as soon as esterified testosterone gets absorbed into the circulation, it is almost immediately converted to active testosterone. From one pharmacology textbook: "after intravenous injection of testosterone enanthate or testosterone, these compounds have parallel pharmacokinetics (Sokol and Swerdloff 1986)." So, in other words, if you inject testosterone enanthate intravenously (I don't recommend this!) it will have the same half life as pure testosterone (4-24 hours). In order to have a prolonged half life of several days, there must be a local depot effect. The blob of oil must remain in place at the injection site (or at least the associated esterified testosterone must remain in place) for many days.
Based upon this line of reasoning, I remain concerned about SC injections. I think the oil stays in place for a very long time. I'm curious if anyone has gotten labs and compared estrogen levels between daily IM and daily SC.
The bottom line, of course, is to get my own baseline and follow-up labs, which is exactly what I plan on doing. But in the meantime I find it interesting to think about such things. I also found some interesting information regarding different levels of aromatase activity in different fatty tissues (thigh and buttock area has much greater activity than abdomen and chest). There is also some interesting research regarding how the viscosity of the oil affects absorbtion--even the preserving agent has an effect on viscosity and absorption. Perhaps one or more of these variables might explain the different experiences on this forum.
Any thoughts? Feel free to criticize my thought process!
I've also been scouring the literature for guidance. I came across a study (Sex Med 201;3:269-279) in which one group of patients was given 100mg testosterone enanthate subq 1x/week, and another group was given 200mg testosterone enanthate IM 1x/week. At steady state, the subq group had a mean T of 896 ng/dL, while the IM group had a mean T of 1659 ng/dL. This is not surprising, given that the IM group was getting twice as much T. The interesting thing, however, is what happened to their estrogen levels. Despite the greatly different T levels, both groups had the same mean E2 level of about 50 pg/mL. In other words, the IM group had a T:E ratio almost double the SC group! Now granted, they were doing weekly injections not daily, but clearly there was some extra conversion to estrogen with the subq group. I assumed this was due to aromatase in the subq tissues.
But the explanation is not that simple. As pointed out by Dr. Saya in another thread, we are not injecting testosterone, but rather we are injecting T esters, and T esters should not be affected by aromatase. Now, I suppose if you inject a big blob of oil (as with weekly SC injections), there might be some local conversion of the esterified T into active T, and then subsequent conversion into estrogen. However, with smaller blobs of oil (as with daily SC injections) I imagined systemic absorption should be rapid enough that there is insufficient time for any local conversion--the esterified T should safely make it into the systemic circulation, where aromatase becomes less of an issue. This line of reasoning would explain both the study I mentioned above, where they used big weekly injections, as well as the experience of some on this forum, where small daily injections made no difference.
Well, anyway, that was my thinking. However, as I continued to look into the research, I realized the picture in my mind was incorrect, or at least incomplete. What I had originally pictured in my mind is that the blob of oil we inject into our bodies, whether IM or SC, is absorbed systemically fairly rapidly. I pictured microscopic droplets of oil being distributed thoughout the body in a matter of minutes or hours. I then imagined the esterified T within these tiny droplets being very gradually converted into active form (by the esterase enzyme--which is ubiquitous in the body). This conversion takes place over a matter of days, leading to the long half lives of T esters (e.g. 8 days for testosterone cypionate).
So this is how I pictured things happening. But I was wrong. This is not what happens. As I said earlier, esterase is everywhere in the body. This means that as soon as esterified testosterone gets absorbed into the circulation, it is almost immediately converted to active testosterone. From one pharmacology textbook: "after intravenous injection of testosterone enanthate or testosterone, these compounds have parallel pharmacokinetics (Sokol and Swerdloff 1986)." So, in other words, if you inject testosterone enanthate intravenously (I don't recommend this!) it will have the same half life as pure testosterone (4-24 hours). In order to have a prolonged half life of several days, there must be a local depot effect. The blob of oil must remain in place at the injection site (or at least the associated esterified testosterone must remain in place) for many days.
Based upon this line of reasoning, I remain concerned about SC injections. I think the oil stays in place for a very long time. I'm curious if anyone has gotten labs and compared estrogen levels between daily IM and daily SC.
The bottom line, of course, is to get my own baseline and follow-up labs, which is exactly what I plan on doing. But in the meantime I find it interesting to think about such things. I also found some interesting information regarding different levels of aromatase activity in different fatty tissues (thigh and buttock area has much greater activity than abdomen and chest). There is also some interesting research regarding how the viscosity of the oil affects absorbtion--even the preserving agent has an effect on viscosity and absorption. Perhaps one or more of these variables might explain the different experiences on this forum.
Any thoughts? Feel free to criticize my thought process!
Last edited:
