I've taken an opiate, carisoprodol, and a benzo on many occasions, but I was not seeking out a 'holy trinity' experience and didn't take them in an optimal order.
When I am getting low on H and I know there's only two shots left at best (and they're going to be on the small side), then I become more interested in getting max value with minimal materials. And I'd go: 150mg pregabalin, 500mg Soma, 1mg alprazolam ( half a Xanax bar) - take them all orally and let 'em sit in my guts for 30 - 40 minutes, and then I'd do my shot. And that worked. Very well. Pregabalin is a powerful potentiator for both opiates and benzos. Soma seems to boost opiates. Alprazolam would hit harder than usual (due to the pregabs, I assume).
Because I would take the H by IV, it'd kick in way faster than the others. So stage 1 was taken all the other stuff orally, then spending a good chunk of time waiting for it to work. By the 40 minute mark, I could definitely feel it in the body. A very loose, relaxing kind of heaviness. It takes some time, but it gets there. So then stage 2 was shoot the dose of H. Now that part came on real quick. Stage 1 takes around 40 minutes for effects, and stage 2 took about 6 to 8 seconds. It would hit hard, with synergistic power. If you happened to be standing up (I have a habit of immediately capping the syringe I just used and wrapping it in some cardboard (like those toilet paper holder things for disposal) and then moving to dispose of it immediately.
I don't want anyone to come into contact with my used syringes - or even see them. I just want to get them out of sight, out of mind ASAP. So I put the cap back on, wrap it in something, and in the bin it goes.
Anyway, the point of all that is that immediately after one of those soma/lyrica / xanax / H runs I once stood up out of habit to put the used spike in the bin, and it all hit me at once and my brain was telling me, in no uncertain terms, that I had about 2 seconds to get myself seated or at floor level. I made it back to my original seat and sat down in time. I didn't move for a good two or three hours after that.
This is just a little story that came to mind when someone mentioned the "holy trinity".
Know what else comes to my mind when I hear that term? HOW FUCKING DANGEROUS IT IS. If dabbling with those drugs (Soma, Benzos, Opiates) if something you must do, get to know each one of them one by one. Then trying combining two of the substances in small amounts (half or even quarter doses) (maybe Soma and opiate). See how you react to each component, and HAVE FRIENDS WITH YOU who can watch you.
I'm not gonna bother saying "Don't do it!". I'll just ask that you take some steps to limit the potential harm you could face, and especially to make sure you that you wake up after. So many people don't.
it was fun 
".
