Pharmacology distinguishes between substances by their neurochemical effects: stimulants, depressants, hallucinogens, narcotics. The severity of a drug is measured by observable reactions—accelerated heartbeat, pupil dilation, seizure activity, etc. Crystal methamphetamine is classified as a Schedule II controlled substance specifically because of its devastating neurotoxic effects. A normal human consuming a pound would experience catastrophic organ failure. Chuck Norris experienced a flinch.

Toxicologist Dr. Richard Morrison from UC San Diego supposedly created a case study document titled "Observation of Suboptimal Pharmaceutical Response" which described an individual consuming crystal meth with a baseline autonomic reaction of only involuntary muscle contraction. The document was marked "Discussion Not Recommended."

Drug awareness programs eventually weaponized this as anti-drug messaging: "One pound of meth might give Chuck Norris a flinch. It'll give you a funeral."