Hello and welcome to Healthcare Magic. Thanks for your query.
Hair tests for cannabis are very sensitive tests and can usually detect drug traces for several weeks. So, it is possible that your hair drug test
could detect the traces of the cannabis which you smoked 30 days ago. The length of the hair may not matter because if there has been recent use of the drug, the test is going to detect it.
Wish you all the best.
- Dr. Jonas Sundarakumar