Is it possible to tell whether pot has been consumed recently

I’ve been assuming for a long time that the current tests used to bust cannabis consummer couldn’t tell apart those who had smoked it recently from those who had consumed it, say, a week ago.
However, I was watching news on TV minutes ago, and they mentionned road testings for drivers. They showed the procedure. Roughly, they stop the car, use a dog to find the drug or bust the consummers. Then, they bring them to the police station where they test their urine on the spot. If the result is positive, they make a blood test in order to know whether the dope has been consummed recently or not (this part was explained/demonstrated by someone who apeared to be a MD or lab technician). Then only they can be considered as DUI.
So, are there or not reliable tests allowing to know if marijuana/ cannabis has been smoked recently?

From what I understand, since the active ingredients in cannabis are fat-soluble, they show up in urine long after the effects of the drug are felt. So as a SWAG, I would say that a blood test would only show positive for cannabis if the subject had those ingredients in their bloodstream.

Man, that didn’t make a whole lot of sense. I meant to say that the active ingredients would only be in the subject’s bloodstream for as long as he or she was feeling the effects of the drug. Which, I’m pretty sure, is not for a whole week after one joint.

They screen Dumb and Dumberer: When Harry Met Lloyd for them. If they laugh, they’re still high.

What if you havn’t done pot in 5 years, and then you consume some? Then you get tested on the spot. Will it show up in a urine sample right away, like during the high?

Most likely. Tentacle Monster is right, the active ingredient (THC) is fat soluable, and takes a while to be cleared. All of the drugs-of-abuse testing platforms I have seen or used give a yes/no answer. An arbitrary value (say, 1000) is assigned to a cutoff concentration (say, 50 ug/mL) of a given drug. Any reading above the cutoff is called positive, regardless of the number; any value below the cutoff is called negative. I have seen results just below 1000, which means that there’s something there, I just can’t call it positive. On occasion I have called an ER Dr. to let them know that there’s evidence of a low level of whatever, but I have to call it negative. That information helps them diagnose or test the honesty of the patient.

Some of these tests are “promiscuous” enough to pick up metabolites. For instance, many cocaine tests also pick up benzoylecgonine, a metabolite. So, while the user may not be under the influence of previous cocaine use, they may still turn up positive on a test that picks up metabolites.


[QUOTE=Tentacle Monster… Which, I’m pretty sure, is not for a whole week after one joint.[/QUOTE]

Not sure about “not for a whole week”, although perhaps the “one joint” bit is relevant to that. My point, such as it is , is that cannabis can show up in test for longer than a week, possibly nearer to four weeks.

I recall several newspaper articles (and sorry - cannot provide links 'cos newspaper sites often restrict searching to people who pay, or simply don’t make it available after a few days) in which the problem of illegal drug use in prisons is addressed.

The gist of such articles was that often people acquire a habit of using drugs other than cannabis in prison, because cannabis can show up in tests for <= 28 days after use. This is presumably not fun for those who use it and have strong opinions against getting found out, and the suggestion put forward was that this means that such people might then turn to drugs that clear out of the “showing up in tests” system rather more quickly.

But I can say I am very sure that cannabis used a couple of days previously, never mind a week, is not likely to render user incapable of proper mental and physical skills.

As for the O.P., I simply don’t know, but, sadly, I suspect not. N.B. am NOT advocating use, merely thinking that it could be pretty silly for someone to be arrested, charged, sentenced because cannabis consumed >=a week ago would be treated in the same way as cannabis consumed that very day.

Reason (not very GQ-worthy, but still… ) I say " I suspect not" is that I think such a development would have been loudly trumpeted in the media (in which we trust) :slight_smile: - yes but that would mean they ought to tell us all which “scientific study” had made all this possible, thereby allowing us all to learn whether such a sensitive test is in existence.

I think the public has a right to know ! :slight_smile:

(That sounds dodgy, I realise, but I’m in no danger from cannabis testing, and I don’t drive a car ( I cannot even afford to make a broken bicycle work), so I have no dog in this race, but am just interested in the the whole logic of it, given that the police are often under pressure of work, and that the court system is pressured by the amount of crimes, whereas one would hope that crimes such as robbing, thieving, attacking, and generally causing harm to the general public would be able to be dealt with on a different level from, say, that crime committed by a person using illegal substance.

Oh, I seem to be going off on a rant, and perhaps a rant full of tangents.

So. I shall stop, pausing only to whine that as soon as anybody makes a law against ?Driving With Dangerous Arrogance? , a happy Celyn I shall be.


N.B. Given that the O.P specified driving , no problem there - I , as a pedestrian, want all drivers to be alert and clever at all times.

There is a blood test for THC. When I worked in bone marrow transplant research, we did a study on the use of THC for nausea associated with total body irradiation. We drew blood for levels every few hours after the THC was administered.