I should have been more careful in my wording.
It is not an MAO inhibitor, although it is a monoamine.
I don't believe there's a risk with other drugs, because I doubt it ever enters your brain--it's made on-site inside your brain, like other neurotransmitters. Instead, I've been talking about what supplements might do to your body.
Arginine is an amino acid, present in all proteins, that you eat everyday. If you take the "acid" part off and keep the "amino" part, you get agmatine. Agmatine appears to work a bit like a neurotransmitter in the brain, and since it antagonizes NMDA receptors, may help prevent the development of tolerance to certain drugs, but as a supplement wouldn't effect this process.
Supplements might effect more peripheral nervous system responses, and help opiates block pain sensations, but I think that is separate from psychological, subjective feelings. I don't think supplemental agmatine would have any interaction with benzos or opiates where they usually concern drug users.
It also has a different role in the body. Arginine, besides being an amino acid building block of proteins, is part of a system that recycles and packages nitrogen waste for removal. That's the urea cycle. Agmatine is part of that, and it exists in a balancing act with arginine. Too much arginine, and your cells make agmatine; too much agmatine, and your body makes arginine.
Then there's nitric oxide signalling. Nitric oxide, NO (not to be confused with the nitrous oxide N2O that your dentist uses) is an unstable, radical gas produced by a stimulus, released into the blood, that causes localized vasodilation. In other words, sexy person strokes your penis, nitric oxide is released, smooth muscle relaxes, blood flows in, you get a boner. Viagara keeps that signal "on".
If a person has clogged arteries that reduce blood flow to the heart, and they feel chest pain (angina) as a prelude to a heart attack, they can take a drug like nitroglycerin that is broken down into nitric oxide in the blood. This dilates those heart blood vessels, and allows more blood to reach the heart, and reduce pain.
Here's the leap in logic: arginine is the precursor to nitric oxide. Bodybuilders have been told that if they eat arginine supplements, it will produce NO and cause vasodilation. That vasodilation will make their veins get bigger and impress/intimidate sexual competitors. There's no reason to think that could happen, since NO production happens in response to a signal, not concentration of arginine. The supplement packaging also never mentions it gives you boners, which it would if that mechanism was real. It would also cause your blood pressure to drop, making you faint, and would kill you if combined with Viagara. So I was making a subtle jab at the bodybuilders, who IMO are taking snake oil. NO is degraded in a matter of seconds or less in your bloodstream, and can't be contained in a supplement. Compounds that break down into NO are obviously prescription-only, since they cause serious side effects, besides strokes and hemorrhage you'd probably at least have a pounding headache.
So, worse for them would be to take agmatine along with their arginine, since if it worked the way they think arginine works, it would BLOCK the effects and prevent vasodilation and poofy bicep veins. They'd be spending money on snake oil that prevents their other snake oil from working.
Now, I don't think it will do much of anything in supplement form. This is stuff you eat everyday, it's in cheese, and your body is very good at preventing food from causing profound effects on your vasculature. No ones gets an MDMA high from eating a hamburger patty, even though it's loaded with phenylalanine, tyrosine, and tryptophan, all precursors for dopamine and serotonin. Instead, I think taking agmatine supplements will just lead to rapid conversion into arginine, and you'll never notice anything.
If you suffered from impotence, taking an enormous amount of agmatine might prevent your Viagara from working for a while. But other than that, I don't think it would effect your health, or that it's worth anyone's money. I should have been more clear that I was making fun of an entire industry.
EDIT: I was also lazy on the angina thing: since nitroglycerin breaks down to produce NO all by itself, it shouldn't be affected by arginine or agmatine. And the coronary artery blockage isn't caused by a lack of NO, but cholesterol scar tissue, so these two supplements don't really have anything to do with it. I bring it up to body builders because they don't see the connection between NO and old people with chest pain or boners, and usually don't take it well.
