I was wondering why certain peptides and amino acids must be injected SubQ and cannot use intranasal or topical routes. The reason appears to be molecular weight. Under 500 daltons allows good topical absorption. Under 1000 daltons permits nasal mucosa uptake. Over 1000 daltons requires SubQ. No handy reference chart existed, so I made one for basic recreational reference only. It is not from a scientific source and may miss a few items since I worked from a general list of what was commonly offered.
SubQ? Intranasal? Topical?
Summary
Why do some peptides need subcutaneous injection instead of intranasal or topical use, and what molecular weight rules apply?
The thread starts with a simple dalton-based chart for choosing routes but quickly qualifies it: lipid solubility matters as much as size, very few peptides cross skin without special aids, and GHK-Cu is a documented exception that works topically. Participants note insulin reaches systemic levels intranasally despite its larger size, while most other peptides do not. The chart is treated as a rough explanatory tool rather than dosing guidance.
What this discussion establishes- MW thresholds given as <500 topical, <1000 intranasal, >1000 SubQ
- Lipid solubility and polarity can block absorption even at low MW
- GHK-Cu and AHK-Cu show clear topical activity in trials and user reports
- Insulin (5800 Da) has documented intranasal uptake
- No peptides reliably cross intact skin without microneedles or similar
Whether any meaningful number of peptides can be considered topically viable or whether GHK-Cu is essentially the sole exception.
Still openPrecise cutoffs and delivery success rates for the majority of listed peptides.
Nothing here is advice.
9 replies · 6 people
↳ replying to @SlowLedger21 (opening post)
Anyone eager for an orange look after putting that amino compound directly onto their body? Skipping it here.
↳ replying to @ClearBeacon24
Haha this cracks me up! 😂😂😂 Blue tint keeps showing up all over these threads... still the thought of GHK-Cu through the nose just makes me cringe. 😬
I'd advise against depending on that basic set of ideas. Smaller molecules with lower weights tend to pass through barriers such as the dermis or nasal membranes more easily, yet this hinges greatly on their fat solubility. A substance that's polar and doesn't dissolve well in fats won't penetrate the skin barrier. Take something like a simple sugar around 180 in molecular weight – it barely crosses the skin at all. Very few if any peptide chains manage to absorb via the skin, except perhaps with advanced tools such as tiny needles, and certain bigger proteins around 5800 daltons can enter through the nose. Without doing extensive looking into it, my estimation is that none of those peptides will pass the skin.
↳ replying to @CopperSignal27
Those two peptides give me superb outcomes on the skin, yet I still have zero experience with the rest of them.
↳ replying to @CopperSignal27
Sure, I see what you're saying. This isn't supposed to serve as instructions on the proper way to give these, instead it's just to explain the reasons certain ones get used differently, basically an overview. There have been plenty of queries in other spots about trying nasal delivery rather than shots for the larger varieties that aren't suitable. I wasn't aiming to spread incorrect details. Sorry if it appeared that way. My mistake.
There were positive outcomes in studies done on people looking at how certain compounds affect skin when applied on the surface. Folks seem to believe they can act that way because they reach the layers underneath. Some checks apparently used very small needle insertions too. This points to a handful of them being able to cross the barrier after all instead of it being impossible across the board. Yet nothing backs up any results from placing them under the skin.
I get really good results from ghk-cu when I apply it to my skin.
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