I might not have the necessary legal knowledge, but I did do some research and as far as I can tell there aren't really any laws preventing someone from taking LSD while in international waters.
Once you get past 24 Nautical miles from shore, you are out of the jurisdiction of any country and in most cases, the law reverts to whichever country the ship is registered to. If, for instance, you make use of a ship under Portuguese flags you should be able to get away with the consumption of LSD.
You might even be able to use a number of other countries as the only laws that really seem to be enforced in international waters are universal crimes such as murder, trafficking, piracy and crimes against humanity.
This could allow for a controlled environment, where paying customers can benefit from the use of LSD while being monitored and cared for by the trained (and sober) staff and crew. Not only would this be an amazing experience, but it could very well lead to a much better understanding of the substance and could aid in the fight to legalize it.
Such a ship could curate activities to enhance the experience, things like meditation and yoga classes or art exhibitions could be available for customers to enjoy.
There are still some obstacles:
1- Even in Portugal, LSD is decriminalized, not legal, which could pose a problem.
2- America seem to follow their own rules in the ocean, so it might be best to stay clear from them, which is a shame because places like The Bahamas and Jamaica could have been the perfect setting.
3- Getting the LSD to the ship would still probably be illegal, I'm not sure if you could maybe deliver it by helicopter from places like Portugal.
4- It would need to be strictly regulated. Any other narcotic substance or an overindulgence of alcohol or one crew member making a mistake while under the influence would be disastrous for the operation.
This idea is not meant to be a party boat, if executed correctly it could be a safe, curated space to enjoy the maximum benefits of this mystical substance which would help us learn about it and potentially use it for the benefit of humanity.
I'm not sure if this would be illegal, but it would be possible to grow the magic mushrooms on the ship
Additionally - terra nullius and space
Povilas SApr 28, 2021
There are also places on land (although very few) that are juridically/politically similar to international waters. The term for that kind of territory is terra nullius.
Antarctica is one famous and best-known example. Even though technically most of Antarctica has been claimed by different countries (except Marie Byrd Land), none of those claims are officially recognized globally, there are no governments to rule and no laws in Antarctica. Of course, taking drugs in Antarctica, while almost certainly being a wonderful experience, would practically be very complicated.
Another quite famous example of neutral land territory is Bir Tawil. It is a small piece of land between Egypt and Sudan that is claimed by neither of them. Being quite the opposite of Antarctica in a sense that it is a hot desert rather than a cold one, it is also much easier to get to.
There also seem to be similar small regions along the Serbian-Croatian border, resulting from a border dispute amongst these countries. One was theoretically proclaimed to be a micronation "Liberland" but is not officially recognized as such.
There might be more similar, lesser know regions in between different countries. Using a neutral land territory would let to establish a more stable, long-term camp for the purpose of legal drug-related research and recreation. A big drawback of taking drugs on the ship is seasickness, those two things don't go along very well, to say the least, in the latter approach this isn't something to worry about.
However, just like with ships the problem of transporting the substances to such a neutral place remains because you have to bring them from one country or another, perhaps the best solution (regarding legality) would be to make/grow them at the place to be consumed only there. The materials required for production/growing are usually legal and can be transported over the borders.
Now space is probably the craziest place to take drugs and for the time being, the most practically difficult, but it's also perhaps the most exciting one, so in the future, such an approach might become quite feasible and desirable. Outer space and celestial bodies have even fewer regulations imposed on them than international waters, at least for now, let's hope this will persist in the future despite growing space exploration/colonization.