How would human culture and civilisation develop if placed onto a planet permanently psychoactive, e.g. because of low (but inevitable) amount of LSD-like substance in either water or air? To simplify, let's assume that the planet is already terraformed, with a reconstructed earth-like biosphere, and that we send humans there without all the technology needed to mitigate the effect (i.e. they have to live as is and use no air filters nor antipsychotic drugs). Or just grow humans with an autonomous space-probe, assuming they will develop some culture on their own.
As previously said, it will depend a bit on if the citizens eventually will build up a tolerance to the substance. And while I'm not an expert, I'd guess humans living in a such environment would have developed kidney or liver like organs all over to body to filter blood before it enters critical organs, or maybe the organs themselves would develop to protect themselves. After all, it's quite unlikely that our bodies wouldn't evolve to handle the environment.
Some fun ideas: What if the effect is seasonal? If the substance is carried over populated regions during rain seasons or rare weather phenomena, the inhabitants might not become immune. This occasional high could cause the citizens to fear rain or water. And there's even the chance that they would enjoy the high and there could be festivities or rituals which happened during these events.
A civilization without the right technology to prevent or analyze these seasons might develop religions to give meaning to the phenomena.
A war-like civilization might prefer to fight wars during these seasons, soldiers might not fear death or become paralyzed if injured.
If the high was seen as an unpleasant phenomena, the civilization might spend all of their resources on trying to fight or avoid it. Maybe they would attempt to pollute the forests or seas in the hope of ending the phenomena. A technology loving society could focus on building hubs which are isolated from the environment, environmental suits or large space stations. Low tech avoiders could try to escape to areas on the planet which aren't as effected and this alone could cause an interesting structure inside the society. Those in power might spend large amounts of their resources in order to live on polar caps, the top of mountains, deserts or deep underground if these places offered shelter from the psychoactive phenomena.
Like lots of drugs, LSD users fairly quickly build up a tolerance. Searching for long term LSD, you can quickly confirm that that continuous LSD usage dosing over a few days results in such tolerance that the result is effectively null. So, for most people, there would be no net effect.
No controlled studies for in utero that I am aware of (they would be unethical) so there could be development issues that are unknown. But it is certainly possible that this could result in more birth defects, etc.
Since the posited scenario would not have acute dosage, the incidence rate of reported strong effects (insanity, flashbacks, etc.) would be very low. A small percentage of the population may experience these however as drugs effects are quite variable.
Over, surprisingly little effect on societal development for environment LSD.
Now, suppose instead of LSD you have a similar drug in terms of psychoactive effect, but that no tolerance is built up to the effects. The effects would depend upon the effective dosage level. I.e., a mild LSD effect would not affect society drastically, i.e., there are lots of high-functional regular drug users. A certain percentage of society would not be highly functional, but since the effects are completely persistent, the society would simply be used to it, i.e., it is just the way it is. A certain percentage of our society is non-functional, we just deal with it. If the dysfunctional population was twice as large as ours, there would not be a significant difference.
If the effective dosage was very high, society would be more like the zombie apocalypse -- very few functional people and they are focused more a basic survival than development. It is still likely that over time, genetic drift would result in an increasing percentage of the survivors would be functional at the high dose rate.
Assuming being under drug influence is not advantaging and evolution keeping the most viable members alive able to reproduce, I think that the society would eventually not be very different from ours. People would merely end up immune and they would certainly develop some biological symbiosis with this compound.
I think that it is unlikely that your population would survive to this though.
Let's suppose all fundamental necessities are freely available and that the population is prosperous.
Let's also assume that the population does not become resistant to the effects or else this question is pointless.
Social co-operation would be limited because of a distorted perception of actions and consequences. For example when Fred does something nice to Bob, does Bob correctly interpret Fred's action? And if he does, does Fred correctly interpret Bob's reaction? If this feedback loop is broken then what social lesson has Bob learned? None.
I would expect that people would behave selfishly and without regard for the consequences; more or less the way that actual drug addicts behave on earth.
No matter the dosage we forget some people affected wouldnt be able to deal with the audible and visual and would need people whove gone through intense 'journies' by themselves to 'show' you how to come back to reality in a good concious mind where the individuals felt safe. Itd be as if you were setting up 'guides' for 'tours'.