My LSD experiences have all been deep dives. I've never taken less than 500mcg and 600-800mcg was normal in my group of fellow psychonauts.
I was once using piracetam, hydergine, vinpocetine and selegiline as an experiment to heal my brain (long story), and took LSD while not knowing the interaction potential. The LSD trip lasted 30% longer and was much more intense, at my usual dose.
For me, IM'ing 20mg of ketamine during an LSD trip was a peak experience. It turned the trip into some kind of hyperdimensional, white-out, angelic experience. I repeated that on five separate occasions and got the same result. My friend and I took turns sitting for each other during the ketamine part because it was very intense. FYI I prefer to IM ketamine because the nasal burning and post-nasal drip would be unpleasant and might send me down a bad rabbit hole while on LSD, whereas I have no fear of needles whatsoever.
I've also experimented with bioidentical oxytocin and LSD. Oxytocin is the hormone of bonding, but also the hormone of nurturing. My friends and I all found that when we did oxytocin before taking LSD, the LSD trip felt unconditionally safe and it created a "nurturing universe" perception, as though the universe was taking care of us. It actually helped me to heal some trauma. We repeated that experiment at least 10 times, to the point that we preferred to take a bit of oxytocin before each trip because it guaranteed the trip would never turn bad. A friend had oxytocin troches made at a compounding pharmacist that dissolved under the tongue. We also used IM injected oxytocin. My friend was on hormone replacement therapy so that's how we were able to obtain it.
I've done NO2 while on LSD and while it creates an utterly florid, out-of-this-reality, visual experience... it really hurt my brain on a physical level. The aftermath felt like how I've felt from fainting, which is basically oxygen deprivation. I felt not right for the rest of my LSD trip, like I was impaired in a way that did not feel healthy. The highly pixelated visuals created by NO2 reminded me a bit of salvia, which I also hated. I would classify these as "low grade mashy highs".
I've taken white grapefruit juice before LSD trips and it noticeably extends the trip. I'm not sure how, since LSD apparently does not have first pass metabolism in the liver (I may be wrong), but the effect was noteworthy. So much so that there were times when I knowingly decided to not use GFJ because I didn't want to extend my trip and feel extra tired. Pink GFJ did not have the same effect.
The best drug combo I've ever experienced was MDA + LSD. I only got to do it once because MDA is imposibly rare in my region, but it was totally cosmic yet heart centered.
