T Nation

Does IM Depth Affect Bioavailability?

Happy Easter.

I’ve been doing my IM test injections to the thigh with a 25 gauge 5/8th needle. I gather this is considered a bit “short” by some, though it’s clearly going into muscle as I have no fat at the area.

I’d like to confirm my assumption that the body absorbs and uses all the oil that makes it under the skin and stays there. I’m not clear on how the test makes it into the bloodstream from inside muscle tissue.

Does IM depth affect bioavailability?

A true IM injection is deep enough that the medication doesn’t “spill out” of the muscle. This depends on both depth and volume of the medication.

If it does “spill out,” some of the medication will absorb into the fat layer above the muscle. If it gets into the fat layer, it will have a much slower path into the blood stream.

Ideally you would go deep into the muscle, like over 1” into the thigh (usually necessary for vaccines). But for most of us on TRT a shallow injection work just fine, especially if dosing multiple days per week where the volume of medication is low.

I will add that from my own experience, a 1/2” needle into the delt gave me the same results as 1-1/4” into the thigh. The delt is shallow IM, and the thigh is deep IM. I felt the same on both.

Short answer is no. There have been at least 2 recent studies that show there is no difference between IM and SC injections in the release and absorption of T. It basically comes down to what works best for you.

I use a 25g 5/8 into the shoulder these days. I used to use a 25g 1 1/4 into the thigh for a year. I draw with an 18g and then pop on the 5/8. Painless and fast. Many prefer an insulin syringe but for me it took too long and the needle got dull after going through the rubber during the draw, hurt more than necessary, for me. Personal preference, we all have our preferred way.

Can you give me links?

Go the tried and true method of deep i.m and you cant go wrong. I dont like shallow i.m seems to be more blood vessels and shit there.

There are a couple posts here and there of joint pain after shallow IM. Sometimes knees, sometimes hip, always the side of the shallow IM site.

I have experienced it as well on a few occasions using 1/2inch 29g in the thigh.

The oil leaks out, perhaps when walking, and travels to the joint somehow. Maybe between the skin and muscle and there no fat there usually in lean individuals. Surely this affects bio availability as some of the T is lost.

This is what I’m curious about. I’m not clear on how the T is absorbed, and figured “if it’s under the skin, it makes it in.”

The body eventually flushes it, and I assume that means it gets into the blood and processed no matter where it is inside the body.

You have completely misunderstood the OPs question which is regarding IM depth. He did not ask for a comparison of IM vs Subq, and you are now hammering this thread with non topic relevant studies. Please create a new topic for that.

To be fair, I’m interested in knowing how to get the most T into action from a given volume injection. To better understand the difference in IM depths (if any), and how the absorption works I welcome comparisons to subQ.

People keep saying that .But what’s to say the T which flows out the muscle doesn’t end up through an excretion channel vs absorption channel? I also want to know the answer.

That’s a great point, I’m as hungry for the answer as my body is for the T.

Ah ok then.

What “excretion channel” would that be? Things get excreted either by never leaving the ailimentary tract…like…say…fiber. Goes in your mouth and out your ass unabsorbed / unmodified.

Other than that, things to be excreted have to get to the blood stream anyway, where they’ll be filtered at some point by the kidneys or liver. If your liver screens it out (which eventually it will), it gets dumped into your intestines for removal.

Either way…the T you inject is getting into the blood somehow…at which point the ester will get cleaved and it’ll go to work until the liver gets around to filtering it out with the trash.

When I had been on once a week for about six months and not having a great time of it, I realized that the way I was pinching my skin was only getting me about a half inch in to my muscle. It was my quad, so not a lot of fat there. When I purposely went deeper with my shot (closer to an inch) over the course of the next few weeks, I noticed an improvement almost across the board.

There is a good chance I was leaking a little T (easiest explanation) although I was always pretty careful to leave the needle in for a bit, and not squeeze it out, etc.

Short answer: I had better success with a deeper shot.

You can’t go by feel for levels. @dextermorgan for example had very high blood levels of T, but didn’t “Feel” it the same as the same dose IM. His blood levels were the same both ways I believe, which would indicate that it has nothing to do with possible “Leakage” or excretion by biologically unknown means. It simply hits different people different ways and there isn’t a scientific study to explain how it “Feels” one way versus the other. It apparently can be independent of your actual serum levels as well. Try the different methods and do the one that works for YOU. It may even be one that gives you a lower actual level on the blood test, which really isn’t important if you like that way better and it works for you.


Ah. So given that OP expanded the question to include subQ…subQ appears to make the optimal use of a given amount of IM injected T. See the studies youthfulguy55 posted. One of them states that a lower mean dose than is typically used IM was able to achieve similar mean serum levels.

Anecdotally, I’ve tried subQ. Don’t like it because I get a painful lump under my skin for days.

Funny story, I’m right-handed and my injections into my right thigh are painless, but I have to reach over to my left thigh and always manage to screw it up. It doesn’t seem to go as deep and there is a localized spot of pain not unlike what you described. Those “botched” injections were actually the impetus for asking about this, as I was worried I was wasting T.

I appreciate everyone weighing in. I’ve decided to stick (get it) with 5/8" needles.

In other news, I’m only two weeks in, and the change to twice-weekly injections has fixed the “dragging ass” feeling I get the couple of days before the next injection. It has also cured the compressed feeling I’d get about 24 to 48 hours after an injection of 200 mgs Cyp, my tinnitus would rage and I’m certain my BP was up. Now, right around the time I’m asking if I feel a comedown, I’m injecting again.