Will I Be Tested Positive Through Hair Drug Test 90 Days Post Smoking?

Posted on Fri, 3 Jul 2015

Medically reviewed by Ask A Doctor - 24x7 Medical Review Team

Fri, 3 Jul 2015 Answered on

Thu, 23 Jul 2015 Last reviewed on

Question : I smoked a small amount of weed over the course of 4 days. A few hits a day, then stopped on the first of XXXXXXX I had a hair test on XXXXXXX 26th. They did not cut the hair all the way to the scalp line, there is about 1/4 inch of hair remaining. I'm told the lab is moderately strict in their levels. There was no use before than for 90 days. Not a habitual user, btw, was experimenting with relief from restless legs syndrome (which worked!). Haven't heard anything from my prospective employer, but I've quit my last job. Needless to say, I'm stressing out badly. Can you provide any insight into my chances?

Answered by Dr. Vivek Chail (49 minutes later)

Brief Answer:
There are chances for a positive test

Detailed Answer:
Hi XXXX,
Thanks for writing in to us.

I have read through your query in detail.
Please find my observations below.

1. Hair test for weed is positive from 10 days after smoking and up to about 3 months.

2. The hair used for testing is till 1.5 inches from scalp. Since hair grows on average 0.5 inches per month therefore in 90 days a person with average growth will grow hair for 1.5 inches.

3. Assuming that your hair grows 0.5 inches a month then it would have weed present in the test sample should you have 0.25 inch hair on you that was not tested. This is because a month had passed since you smoked weed. Therefore a positive test is likely in your case.

Hope this answers your question. Please feel free to correct any oversight in my interpretation of your problems and discuss them in detail as per your requirements.

Hope your query is answered.
Do write back if you have any doubts.

Regards,
Dr.Vivek

Above answer was peer-reviewed by : Dr. Vaishalee Punj