I’m suspicious that there are no readily-available recreational mind-altering substances that are good for you. Were Huey Lewis and I just born into the wrong reality?
Some studies indicate that moderate consumption of alcohol is beneficial.Cite. The emphasis is on moderate, however.
And electric brownies are high in fiber.
Regards,
Shodan
By “good for you” do you mean nutritional, or just beneficial in some way? If the former, I don’t see any reason why any should be. But it is worth mentioning that nutmeg contains a mild hallucinogen, and I’m guessing (though I really don’t know) that hallucinogenic mushrooms probably also have some nutritional benefits in common with the edible but non-hallucinogenic varieties. And anyone know the nutritional make-up of morning glory seeds? Actually, I’m guessing if you probe more deeply there are probably plenty of plants and seeds and herbs that contain both hallucinogenic and nutritional components.
And if you meant the latter, well, that’s a much larger discussion probably better suited to GD. I will say that, though Huey Lewis’ demands are quite restrictive, there are some drugs out there that come close. 
Michael Pollan discusses Marijuana at length in his Botany of Desire book.
It depends on what you mean by “good for you”. Opiates relieve everything from chronic pain to panic disorder yet people that abuse them end up taking everything from heroin to oxycontin that usually cause great harm in many ways. The problem with the whole concept is that, used recreationally, most drugs push the brain and/or body to the limit and that either results in addiction or other adverse affects.
Marijuana can meet the conditions in your OP. California was serious when they passed their medical marijuana law. It isn’t physically addictive and it can help everything from glaucoma to chemotherapy patients. LSD isn’t addictive either and many people report some kind of spiritual revelation from it.
I can attest to the non addictive part of that. It never caused any spirtual revelations but it certainly helps you to realize your place in the universe.
Not so much. The good doctor does agree it appears to be good for other things, though.
Money has been known to alter my mind with no observable detrimental side effects 
What does readily-available mean? OTC, prescription, or illegal but easy to get?
What does ‘good for you’ mean? Nutritious, therapeutic for disease or injury, or just makes you feel good without causing any harm?
Different psychedelic drugs have different degrees of benefit. The organization called MAPS (multidisciplinary association for psychedelics studies) is sponsoring a variety of studies on LSD, MDMA (ecstasy), psilocybin (mushrooms), and ibogaine as therapy for things like cluster headaches, post-traumatic stress, psychotherapy, and treatment of opiate withdrawal and alcoholism. I would call that ‘good for you’. It has to be said that none of these substances are child-safe, but the supposed harm is generally wildly exaggerated when it isn’t outright fabricated. You can read more about MAPS and the studies it conducts here: http://www.maps.org/.
As for the non-psychedelics, of course most of them came into existence because they had at least one legitimate use - for example, heroin can be a blessed angel of mercy for someone in extreme pain, although I think we can all agree that it doesn’t fit in the ‘good for you’ category.
By readily-available I meant legal and, well, readily available.
By good for you, I meant ‘not bad for you’. By ‘not bad for you’ I mean not destructive in some way to your mind or body or spirit.
You buy it at the store. You injest it. You get up or down or all-around. You go to bed and sleep well. You wake up refreshed. You’re no worse off than before you took it.
The only thing I can think of is moderate alcohol consumption. Depending on your weight and sex, you could drink one or two (maybe a little more in some cases) drinks a night and not suffer any problems and maybe have some health benefits. If you are a male, two drinks every day shouldn’t hurt you and may be considered recreational for these purposes. You could do that every day like some Europeans do forever without incident. The risk of escalation and then eventual alcoholism is always a treat for certain people however.
A lot of people really love caffeine and are technically addicted to it although I will never understand the appeal. Caffeine doesn’t cause much harm or none at all.
Endogenous endorphins are opiates released through strenuous exercise and that may be a good thing.
I don’t see why marijuana wouldn’t fit this description, except for the buy-it-at-the-store part. Unless you take “illegal” to mean “bad for you”, which I don’t.
Tea?
The problem is that governments tend to* make anything stronger illegal as a reflex. Are all the substances in this list dangerous? Of course not, but they’ll all illegal in the UK.
- by “tend to” I mean always.
Well, the “legal and readily available” part is the problem. However, I can actually think of a couple:
Dextromethorphan is a common OTC cough suppressant which, in high doses, becomes a dissociative hallucinogen.
NO2 (nitrous oxide, aka - laughing gas) is readily available in the form of small cartridges easily obtained at many home appliance stores, sold for the purposes of making your own whipped cream.
Salvia Divinorum appears to still be legal, though likely for not much longer I would guess. It’s not exactly readily available at your corner drug store but not too difficult to obtain online (or at least it wasn’t some years back when I was into all this stuff).
In general, governments don’t like psychoactive substances to be “legal and readily available”. I’d say in most cases, the best hope of a psychoactive substance remaining legal is for it to not be readily available.
Except for the part where it makes you vomit profusely and gives you the second worst diarrhea you can imagine, all at the same time. If you extract the DXM, and then ingest it, I’m sorry. You won’t be able to talk, take a drink of water, or even smoke a bong. And you don’t feel so great the next day, either, having left all of your insides in the bathroom. YMMV
Also, it almost doesn’t really meet the OP’s criteria of legal and readily available, as it is illegal to use the product in a manner inconsistent with its labelling, as well as pretty much impossible to find without being mixed with guaifensin, which will make you even sicker than the DXM itself, as that is part of the reason it is there.
Sorry, but I really hate the stuff! It helped teach me that pharmaceutical misuse is lame.
Not to mention most commonly mixed with either a halogen that makes you feel chemically loagy the next day or a plastic that the last time I used it (for a cold) only exacerbated the cleansing of the bowels (and makes the concentration for altered state of consciousness harder by time-releasing.)
Well, it’s been over 10 years since my one experience with the stuff, so I’m certainly not the most reliable source of up-to-date info, but I can say that:
- When I did it, it was most certainly available without guaifensin (although it is certainly much more common to include it). I think Tussin’ was the brand.
- I didn’t vomit, nor have diarrhea (to the best that I can remember, which admittedly also isn’t all that reliable, though I did feel a bit hungover the next morning.
- Not only was I able to talk, I struck up a conversation with a stranger sitting next to me that lasted for hours (and I’m actually a very shy guy), so it actually greatly reduced my inhibitions.
Don’t get me wrong, I ain’t recommending the stuff. My experience wasn’t bad, but I haven’t had any impulse to re-create it in my more adult years. It’s actually a pretty crappy high as drugs go. But based on my experience, I think it can fit the OP’s criteria (assuming that it is still available without any other active ingredients. If not, I retract).
The question of “readily available” reminds me of the Simpson’s episode (at LEAST as reliable as Wikipedia) where Homer is injured and is offered medical marijuana by the doc. “But, isn’t marijuana illegal?” he asks. “Only for those who enjoy it,” is the answer.
Not entirely harmless though… it starves your brain of oxygen, and I understand people have asphyxiated themselves from using it incorrectly.
Extremely easily available. I tried it and I found it very interesting, but then I like going deep. I could easily see it freaking someone the fuck out. Personal reactions vary widely… definitely it isn’t your gentle-buzz-on-Friday-after-work sort of thing. I don’t know of anyone who has tried it more than 2-3 times before moving it on. Blessedly, it’s short-lived though.
DXM - another thing that takes you inwardly pretty deep. Not conducive to hanging around with a buzz.
cite?
BTW, here’s Cecil on the subject.