I've never heard of genetic tolerance, but it's definitely interesting and I looked it up. It's definitely a thing you'd need to look out for if you eventually choose this path.
It's worrying, but for me I don't really believe that it'll be much of a problem. I've gotten really skinny overtime and the less weight the better in my opinion because there will a higher concentration of the drug in your blood floating around to your brain.
Take a look at this:
https://www.nature.com/articles/s41598-022-21003-y
You can summarize it using some random AI tool because it's a lot to go through.
Here's what I got from it:
- CYP3A4: Gene that makes enzymes breaking down fentanyl faster.
- CYP3A5: Gene similar to CYP3A4, also breaks down fentanyl faster.
- ABCB1 (MDR1): Gene that pumps fentanyl out of the brain.
- OPRM1 A118G: Variant of the mu-opioid receptor gene that reduces receptor response to fentanyl.
Even if you're unlucky enough to have a genetic tolerance to opioids. A large amount of fentanyl will still most likely be effective if you do it in a place where you know people won't come checking in at for a while.
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This is a recent 2025 National Drug Threat Assessment released by the DEA.
(
https://www.dea.gov/sites/default/files/2025-05/2025 National Drug Threat Assessment_Web 5-12-2025.pdf)
The average has dropped in a couple of years, but it hasn't reached single digits yet. So getting fentanyl that is 1% pure isn't always a common occurrence.
It's always best to test before using. If the purity is very low I'd assume that the test will most likely turn back negative for fentanyl on the first test (Please correct me if I'm wrong). If the purity is average then first test will probably turn out positive. Again this is just an assumption. There's companies out there that have a service for testing the purity of a certain drug and what that substance actually contains. They use Gas Chromatography to test out the purity. It's similar to the one they used in breaking bad if you ever watched the show (
https://www.youtube .com/watch?v=6EU-EfKHwY4).
There's a company called energy control based in Spain that lets you send out a sample of 50mg in powder for 120€ to test out both the substance and the purity. Of course, this is very expensive and I think it's not necessary but it's there if you're wondering (
https://energycontrol-international.org/drug-testing-service/submitting-a-sample/).