Well, for starters I'm glad you did a cold water extraction on them to get rid of the Tylenol because that stuff is hard on the liver. Back when I was just eating pills to get my opioid fix I didn't care and would eat handfuls of 'em, Tylenol and all and by all rights should have a bad liver. I'm lucky, didn't do too much damage. The cold water extraction will do nothing for potency I'm afraid.
Next, what I recommend here is just what I've done in the past and experimented with. It's not necessarily advice to be followed. I don't want to be responsible for putting someone's health in danger. But, I can tell you what I know and works for me.
What's your tolerance like? Have you been using opioids for a while? If you have a high tolerance then even eight 7.5 hydros aren't going to be too terribly powerful with or without adding something in the mix. By the time I wound up moving on to dope it would take me twenty of those things to even feel "right".
Anyways, to increase potency there are a couple of things you can try. The easiest is to take a Benadryl or two before ingesting the hydrocodone. It'll add to the depressant effect and also kill any itching that comes along. Also good for nausea.
If you can get your hands on a prescription of the nausea med Phenergan, that's a sure fire method. Works along the same lines as the Benadryl only it's even more powerful and REALLY kills nausea. Might even get some nods on it depending on your tolerance. Back when I ate pills I wouldn't do it without a Phenergan. Be warned though, the Phenergan will leave you with a mild hangover after all is said and done.
You can also try drinking a couple glasses of real, fresh grapefruit juice. Not the artificial stuff from a gas station but the real deal from a quality grocery store. The grapefruit juice can increase the bioavailability of the hydrocodone in your system after you ingest the pills. It works on a particular enzyme that is responsible for the metabolization of such chemicals in the system. Some say this only works for codeine, oxycodone, and morphine but I've noticed a difference in the past.
You might also try taking a Tagamet pill. It's an OTC heartburn med that also helps with the absorption and bioavailability into the bloodstream of the chemical.
Last but not least, if you have access to a benzo like Valium or Xanax, taking one of them can really increase the depressant effects of the hydrocodone. But, if you have no or little tolerance than PLEASE don't consider this as it can lead to serious respiratory depression which can well, can kill ya dead right quick! Even with a tolerance it can be dangerous so just be very careful.
Those are the methods that I know of and have used in the past. I hope that it helps and you can get some use out of it. Glad you're posting on BL, this forum is awesome! Have fun, I hope one of these methods does help you get better results but above all PLEASE BE CAREFUL and play it SAFE. We all like to feel good and love our chemicals but the name of the game is doing it safely without harming ourselves or others! Hopefully I'll see you around on the forums and if I can help more just let me know. Peace!
