Opioids definitely help to make trips more euphoric and calmer, but they will definitely not stop it, in my experience they don't reduce the intensity so much as make you feel good, so anxiety and negativity are lessened. But if you're freaking out they're not going to help. Benzos can be used to pull yourself out of a panic situation, and will bring the trip down but not totally kill it. An antipsychotic will stop a trip in its tracks, but IMO this should only be done if you've lost the plot (in which case it would likely be someone else administering it). Also antipsychotics are nasty drugs with a lot of bad side effects so should only be used in emergencies. Honestly it's best to ride a difficult experience out, you will be much more likely to gain something from it if you work through it. Killing a trip suddenly can leave unresolved trauma behind.
One time I took a full dose of AMT at a music festival, and then added 4 hits of LSD. I was watching a band, and the lead singer had a bit of a tantrum towards some of the other band members, and it made me feel really awkward. I left and found some friends at a different stage, where Steve Earl was doing a sound check. He got really pissed at the sound guys and started screaming FUCK YOU MOTHERFUCKER and stuff to them, it was really intense, and then some people started leaving because he was being a douche, and he started screaming FUCK YOU COME BACK HERE MOTHERFUCKERS at them, and the vibes got really bad and I started to feel The Fear coming on. I left the stage to head back to my group's campsite. I was tripping so hard that everything I imagined in the darkness I saw, I had no idea what was actually in front of me. Someone helped me across the bridge over a creek, and I went to my tent, in the grips of this feeling of immense existential terror. I pulled out my etizolam bottle and dosed 2mg, and realized as I swallowed that I had just dosed 2mg of DOC from my identical-looking DOC bottle, I couldn't read the labels in the dark. Then I really started to freak out. I pulled out the real etizolam bottle and dosed 2mg, and laid in my tent in the fetal position trying to fight off the feeling that I was falling into eternal madness for 20 minutes, and then it kicked in and within 10 minutes I felt amazing, I was still tripping really hard but less so, and I was straight back to having a great time. After a while the DOC kicked in and I spent the next 2 days in a blissful psychedelic storm... took 2 more days to feel baseline, and it was one of the most fun trips I've had.
Point being, benzos do have their place and can be a lifesaver, even though I save them for that sort of situation, where it's not worth trying to fight through it, nothing good would have come from that. But even though I was panicking, I was still in control of myself... if I had gone psychotic and lost it, I'm not sure etizolam would have done the trick.