I'm sure the confusion is mine, but are we getting mixed messages on whether HGN is valid test for drug use? At TDCAA Summer Seminar in Wichita Falls in Aug 02, my notes say HGN test positive only for alcohol, brain stem injury, and one kind of DIP drug. But the article in the most recent Prosecutor seems to say HGN is valid test for other drugs as well. Our local LEOs have got it in their heads that HGN is valid test for marijuana use. I think they are wrong. Can someone give the authoritative word?

From everything I've read my understanding was that HGN could not validly be used to determine whether or not a person was under the influence of marijuana. I can't remember seeing a study where that premise was validated.

Here are a couple of references that I pulled up that suggest that it cannot be used:


DRE Information

Indiana Department of Toxicology Report

Robert DuBoise

I have the 1993 manual published by the U.S. Department of Commerce and NHTSA entitled "The Drug Recognition School". Part of the DRE testing involves not only the HGN but also four other eye tests: vertical nystagmus, lack of convergence, pupil size, and pupil reaction to light.

According to the manual, HGN can recognize "CNS Depressants", PCP, and "Inhalents". It cannot detect CNS Stimulants, Hallucinogens, Narcotic Analgesics, or Cannibis. (Chapter V, Page 1)

Hey, I don't vouch for it - it's just what my government tells me.

Many types of drugs are CNS depressants, so the answer is that some drugs can create HGN in addition to inhalants and PCP.

CNS stimulants, hallucinogens, narcotic analgesics, and cannabis do not create HGN.

The cannabis confusion (no pun intended) is in "lack of convergence." This test is also "an eye test," so it may be confused with the more common "eye test," the HGN. Cannabis is the only drug that I am aware of that does not create HGN, but does create lack of convergence.

while looking for that "lack of convergence" thing, how about noting the eyes looking like a new york city street map all in red?

btw, i have several officers i consider more knowledgable than others who tell me that a person who has recently smoked mj will have green-tinged swollen taste buds: green for the obvious reason, swollen because mj burns very hot. anyone else using this?