[trappedintime]

The experience you will have is tremendously dependent on a few things: your existing state of mind, the physical environment / location of the experience, preparations (if any) made for the experience, and arguably most importantly (IMHO), your intention or reason for seeking the experience.

If you go at it with the attitude that this is simply a reason to get high, or to observe visual disturbances for the sheer sake of hallucinating, there's a very good chance that will comprise your experience. Conversely, if you set an intention of learning about yourself, life, death, existence, the universe, etc., and approach it with regard, then there is a very good chance you will have that experience.

From what I have gathered observing myself and my friends, the latter can be quite transformative to the self. It can encourage profound positive changes in attitude and improve quality of life, increase spiritual awareness and feelings of interconnectedness, greatly diminish or eliminate one's fear of death, among other things. These feelings can last, sometimes for life, and it can take months to fully integrate the lessons learned and information gained after returning from the "journey". See the John's Hopkins study on psilocybin for more information.

Preparation and intent simply cannot be understated when it comes to the use of these substances. What the psychedelic enthusiasts refer to as 'set and setting'.

[thescribe]

If the effect only manifests when you think about it correctly, is it a placebo?

[trappedintime]

And this is precisely where trying to measure a unique experience with microscopes and well-established materialist scientific theorems begins to fail us. An experience, by the way, that many call the 'most important' of their life. They describe it as 'noetic' in that it seems more real than ordinary consensus reality, and 'ineffible' in that it cannot be successfully described, it must be experienced firsthand.

These aren't just the waxings of a hippie distracted at work, I can point you to studies that demonstrate the repeatability of it all (i.e., 'most important experience of life' claims, noetic properties, ineffable, etc.) Many people use these descriptors when regarding their respective psychedelic journeys.

In my opinion, the reason some people have awe-inspiring life-changing experiences and some just see neat visuals or have the ominous 'bad trip' goes back to my first comment. Set, setting, and intention are absolutely everything with these substances. The stuff just seems to be of a higher order, and it seems it gives you just what you deserve.

[pixl97]

When people watch scary movies, why is it they are more likely to have a nightmare afterwards?

Our brain chemistry is exceedingly complex. Also, our emotional state primes our brain with other chemicals. Fear can produce a rush of adrenilne, for example.

So yes, thinking about it 'correctly' changes your brain. Your brain is a chemical reaction, so adding another thought modifying chemical is likely to have different results based on the chemicals already there.

[TimPrice]

Cognitive distortion may manifest in many ways, like bad trips.