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You are here: Experts > Health/Fitness > Pharmacology > Pharmacy > THC absorbtion/elimination
Pharmacy - THC absorbtion/elimination
Expert: Dr. Ravindra Bhaskar Ghooi - 10/30/2009
Question
QUESTION: I am a lawyer. My client was ordered not to consume THC. He was tested immediately after the order and the urine test showed him positive for THC > 300 ng/ml. So, all we know is that it was higher than 300 ng/ml. Then, 32 days later he tested positive again at 150 ng/ml. He is 21 yoa, 6'1, 188lbs. The prosecutor has taken the position that his levels should be considerably lower, or completely eliminated after 30 days. Therefore, this recent test is proof that he has used THC since his original test. So - is the prosecutor correct. I've read that elimination is approx 50% every 8 days. So he would have to be way over 1000 ng/ml. Is this plausible. Just looking for some feedback. Thank you.
ANSWER: Hi Robert,
I am glad that a lawyer is taking some interest in drug testing and drug levels. Far too many people in the US are in trouble because of inaccurate testing, false positive reactions and the like. One of my correspondents has formed a self help group to fight this problem. May be you would like to represent them too! If yes, let me know I will provide her contact details.
Now coming to the half life of THC, it is variable and ranges from 20 hours to ten days. It is therefore very very difficult to calculate what the level should be after 32 days for your client.
However your client had 300ng in test #1 and 150 ng in test #2, this means the level reduced to 50 % in 32 days. The half life (if he has not taken another dose) is 32 days! Which appears a bit too high from reported values.
My opinion is that your client has taken a dose of THC, though I have no absolute proof but the allegation seems to be justified. Your clients half life falls way beyond the reported half lives and that seems to be the problem
Ravi Ghooi
---------- FOLLOW-UP ----------
QUESTION: Thank you for the reply. Your answer assumes that his level was 300 ng/ml at test #1. The reported value of test #1 however, is > 300 ng (that's the cut-off for the test) - so, he could have been 500 ng or maybe 2000 ng - we don't know. If we use this half-life calculation of 50% every 8 days, I guess he would have had to have been close to 2000 ng at test #1. Is that right? Can someone get to a level of 2000 ng? Last, I mis-spoke, his second test was 105 ng, not 150. Does this change your opinion? Is this 1/2 life calculation relatively reliable? Thanks.
Answer
Hi Robert,
Yes the first test result was misinterpreted by me. Under the circumstances that his level was higher, let me give you a list of possibilities that could have led to a level of 105 ng on day 32. Nobody really knows what happened, and as I understand we will never know it. What you require is a bsis to prove your clients innocence and now I believe, (with the new levels provided) you have adequate ground to defend him.
Assuming a half life of 8 days
Day 0 (First test): 1680 ng
Day 8 840 ng
Day 16 420 ng
Day 24 210 ng
Day 32 (Second test)105 ng
Assuming a half life of 10 days the situation will be as follows:
Day 0 (First test): 1000 ng
Day 2 840 ng
Day 12 420 ng
Day 22 210 ng
Day 32 (Second test)105 ng
I believe the second scenario is the one you should insist on.
Half life is extremely reliable, but the half life varies from person to person for some drugs, then we cannot say for certain what the half life would be.
Best wishes to you both
Ravi Ghooi
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