Dear Science,
Can I actually build immunity to iocaine powder, or a similar
substance that isn’t made up?
Battle of Wits
Yes, depending on the substance, but only to an extent. The body
can deal with toxins and poisons in a few different ways, most of which
can be amped up with lucky genetics or some training. Still, you
shouldn’t count on them to win a contest with a Sicilian when death is
on the line.
Antibodies produced by the immune system can grab up the toxin; this
is how the tetanus vaccine (among a few others) works, capturing the
tetanus toxin before it can cause damage. The senses of smell and
taste, particularly the bitterness receptors, are decent at detecting
many poisons; barfing is your next line of defense—a plus for
survival, but a loss on style points. Another neat trick is to eat
something like activated charcoal, which will capture the poison in the
gut.
If you don’t barf, don’t have protective antibodies against the
poison, and don’t have something else in your gut that’ll absorb the
toxin first, the gut will transfer it into the blood. Still, all is not
lost. Almost all of the blood from the gut first goes to the liver
before hitting the rest of the body. The liver lives for this
moment. As the blood trickles through the organ, legions of enzymes
tweak almost all of the molecules and proteins absorbed into the
blood—including most toxins. The CYP450 family of proteins is
the key to victory—the major enzymes that protect you against all
manner of toxins. Past exposure to poison can increase the amount
and activity of these enzymes; thus, this is a way you can gain
protection from a poison through prior exposure.
Ever wonder how chronic alcoholics can drink that much? Why
does the Pill stop working when you take certain antibiotics? By
turning up or down CYP450 enzymes. Your liver treats most medications
like poisons, processing them with the same enzymes. As the number of
drugs has increased, so has the number of weird interactions through
the liver. Mevastatin, a cholesterol-reducing drug, is
safe—unless you happen to be eating red grapefruit while taking
it. The grapefruit inhibits a key CYP450 enzyme used to clean up after
the drug; without the enzyme, the mevastatin builds up and starts
destroying your muscles. Bizarre. Drug interaction is one of the more
artful ways a physician can kill you.
So, if you wish to become immune to a poison, start designing
vaccines or playing with your liver. In theory, it might work.
Science recommends neither activity. Fencing or feats of strength seem
a wiser choice. 
Inconceivably Yours, Science
