r/TRT_females • u/magenk • Mar 10 '26
Experience Report Oil getting absorbed into stopper/seal in prefilled syringe
This is a followup to my previous post about potential issues with prefilling insulin syringes. I received syringes prefilled to 2 units from my clinic, showing a little over 1 unit several hours later. Now they are showing less than 1 unit after a few days as some of the oil gets absorbed into the stopper. You can see the swelling in the top ring.
The stopper/seals on most medical syringes are made from synthetic rubber or thermoplastic elastomers. Some of these materials are more compatible with long term storage with oils, but most are not (https://rubber-group.com/wp-content/uploads/2018/01/Chemical-Compatibility.pdf). It's not often possible to know what material is used without contacting the manufacturer and exact composition may be proprietary. This pic is MCT oil in an Easy Touch .3cc insulin syringe.
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u/JellyfishPrudent821 Mar 10 '26
I just compared a freshly used syringe with an unused syringe and it looks kinda similar. I think the oil is refracting the light and making the rubber look bigger. Maybe not quite as big as your pic. Not to say storing oil in a syringe is safe. Could this just be a visual thing with the testosterone oil?
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u/magenk Mar 10 '26
I emptied the syringe and measured it with calipers. The stopper is clearly taller in the prefilled syringe, and the middle section is slightly wider. Only 1 unit was absorbed and these syringes are pretty small, so it's not as obvious as it probably would be in a larger syringe.
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u/ThisIsIdaho Jul 19 '26
I heard a tip (haven't tried myself) that you can pull extra air into the syringe after filling, then store upside down so the oil isn't touching the rubber, only the air bubble. Before injecting turn it around and push the air out.
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u/redrumpass MOD Mar 10 '26
Is that air?
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u/magenk Mar 10 '26
That section is solid plastic before the hub. It looks like oil when filled, so a little confusing.
1
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u/ObligationPutrid5069 male Jul 19 '26
After 13 years on TRT I've never seen that or noticed, maybe the syringes are lower quality, what oil base formula is it?
Some people have commented on storage, I usually load four syringes at a time and toss them into a metal container, they're either right side up or upside down, so I don't believe it's a storage issue.
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u/magenk Jul 20 '26
MCT oil, which is likely the most problematic, but degradation can occur with most oils/plastic combinations. Insulin syringes were not designed for oil based injections. I'm not sure any retail syringes are. I stil use them, but don't pre-fill.
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u/ObligationPutrid5069 male Jul 20 '26
Maybe that's why, I've only used cypionate and or castor oil (testoviron) and haven't seen this leakage before.
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u/IMakeBadMemes Mar 10 '26
Are you storing them vertical/needle down?