Everyone is different. Some people get fucked on everything they take, others are the opposite, like me. I'd say acid, xtc, and pot are like therapeutic drugs for me. They level me out. I so wish I could be prescribed LSD. It's helped me achieve a lot and get over my petty fears. I'd say stimulants are the least likely to fuck most people up, but then again you don't learn anything from them. In the long run they can give you shit like schizophrenia and paranoia, too. Better not to get addicted to them.. I use them once every few months.
I think cannabis might be what he's looking for. It opens up your mind and gets you thinking and perceiving things in a different way. Just lie back and let the little thought trains go where they want. Look at old photographs and let your mind wander back in time to what it was like in that captured time frame... I'd love to try raw opium sometime! I've heard it's not as potent as a pharmaceutical, but it's got the full range of opiates and must have a more natural and fulfilling glow to it. How about some opium dipped Thai stick?! Just a couple ideas.