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Pseudoephedrine's formula is: C10H15NO and methamphetamine's is: C10H15N. The only differ by an oxygen molecule yet have different effects.

The reason I ask is because I have a relative in the States who suffers from narcolepsy. He used to live here in Europe and the doctor couldn't give him anything stronger than pseudoephedrine/ephedrine to treat his daytime fatigue. It worked but wasn't as strong. When he moved to America, a physician there put him on Desoxyn, the brand name for methamphetamine hydrochloride. He anecdotally reported that it was incredibly potent, much more than the pseudo he took before.

How is this possible? Not only is methamphetamine more potent than pseudoephedrine but it induces intense euphoria compared to the latter drug.

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    You breathe about 400 ppm of carbon dioxide (CO2) every day of your life without harm. The same concentration of carbon monoxide (CO) would be lethal within 2-3 hours. The only difference is a single oxygen atom.
    – Carey Gregory ♦
    Jun 20, 2021 at 14:43

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This question is like saying that a log cabin is almost identical to a skyscraper - they’re just buildings, and many of the parts used in one are also used in the other - they’re just arranged differently. For example, water (H2O) is only one atom different to Hydrogen Peroxide (H2O2) - and you certainly wouldn’t want to be drinking that.

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  • no, it's not really like that at all
    – user16606
    May 7 at 11:29
  • @uhoh It may be an exaggerated example but it's not inaccurate. Pseudoephedrine and methamphetamine are two distinctly different chemicals that happen to share a similar structure. A log cabin and a skyscraper are two distinctly different buildings that happen to share a similar structure.
    – Carey Gregory ♦
    May 7 at 16:35
  • @CareyGregory I think then a better analogy might be an institutional kitchen vs a large public washroom -- similar sizes and gross structures like all-tile or stainless steel washable surfaces and (ideally) ample plumbing and lighting, but very different functions. (I guess some might consider something exaggerated to be by definition inaccurate while others might see room for exceptions, log cabin vs skyscraper involves several orders of magnitude difference in volume, differences in utilities like electricity, air-conditioning, elevators, parking garages...)
    – user16606
    May 7 at 19:35
  • For me I see this as more of a "clever-sounding" comment than a proper Stack Exchange answer. A better answer would actually inform readers how and why similarly sized and similar-appearing molecules can have very different chemical reactivates and how this is important for both the pathways the molecules experience after ingestion, and how they interact with their final target. This answer doesn't even attempt to begin to inform readers in my opinion. To me, it just tries to sound clever. I think it should therefore be moved to a comment.
    – user16606
    May 7 at 19:44
  • @uhoh If this were Chemistry.SE I might agree with you, but it's not. If you want an explanation of why two chemicals with similar structure may have very different properties, that's the place to ask, not here. And yes, the two things are orders of magnitude different, but the comparison still makes the point even if it is in a bit of tongue-in-cheek manner. In any case, the question is almost 2 years old and has more downvotes (+1/-4) than this answer (+5/-2). I'd be more inclined to close the question for lack of prior research than axing this answer.
    – Carey Gregory ♦
    May 7 at 21:33
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I'm just assuming, but my guess is because Methamphetamine is able to cross the blood brain barrier unlike Pseudoephedrine, which cannot. But that's not the only possibility why one drug is so much stronger than the other. The way molecules rotate polarized light also seems to have an effect on how the body reacts to it. Such as L-Methamphetamine (levomethamphetamine) was or is sold out right in Vick inhalers, but does nothing to the central nervous system. Unlike D-Methamphetamine (dextromethamphetamine). This part is just a total guess... but since the only difference is an oxygen molecular, I'd guess that would have something to do with how the body consumes the molecular. So jumble all that together and you're a lot closer to your answer. I know it's impossible to do a simple search for this information, because web results contradict each other and most just label it all just bad and is utterly useless for gaining an understanding. Hydrochloric acid isn't something you'd want to consume, but most pills are the HCl salt form of a drug. Such as pseudoephedrine medications. Cause clearly your question is comparing a log cabin with a chimney to a log cabin without a chimney.

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