Codeine 100% as long as you 1) Know that it is codeine 2) Dose appropriately Addiction and overdose are your concerns but OD on codeine takes a bit
Nitrous oxide -- Drains B vitamins and all kinds of other stuff - especially if you are doing "Whippets" not a regulated steady nitrous to oxygen ratio. Also black out and smash your head quite often. People have been known to seize.
MDMA --- The MA stands for methamphetamine -- but really the main problem is MDMA is usually cut. You got and know how to use marquis reagent it is only MDMA -- still more dangerous than codeine but not that dangerous
I'd disagree, codeine is the most dangerous one out of the three in my opinion.
Codeine increases histamine (known to increase cancer risk) and makes you constipated. Constipation is one of the most dangerous and overlooked problems in health. It causes all kind of downstream problems when your body can't remove waste properly.
Now obviously, either of these three drugs is fine to use once for healthy people and won't instantly cause problems provided they know what they are getting themselves into.
Your argument about Nitrous Oxide "draining" (from my understanding it more limits your body's ability to use vitamin b12, but i suppose that is a bit of semantics) B vitamins is true, yet for a healthy person this is absolutely not a problem.
Someone with a vitamin B deficiency could instantly come into trouble with Nitrous, same with say someone with a serious alcohol problem. Most people will be absolutely fine doing Nitrous Oxide a few times though.
I'd say addiction-wise codeine is also the most dangerous; a person that is finding himself in a bad spot in life is more likely to enjoy and find an escape in the opioid-high/warmth that codeine provides.
While MDMA and Nitrous Oxide certainly can be used to escape reality, they also allow the user to see their lives in a different perspective and gain some insights that might be useful even when sober afterwards.
My ranking for safest 1 time usage would be:
1: Nitrous
2: MDMA
3: Codeine