Hi there ~
I understand your concerns. And I believe your concerns are valid because you are taking a drug test
to start an internship. I am also assuming that when you say you smoke a little bit, I think it is marijuana you are referring to. I believe that the drug may be found in hair sample for a long time after they are out of your system in the blood which is about 1-3 months, depending on the usage. It may be helpful to have a haircut, but getting any shampoos or conditioners to help, either legitimate or illegitimate are not going to be helpful. I hope this helps allay your anxiety
and you might want to get a test yourself before you get tested by the company to relieve your anxiety.
I hope this helps. Take care and have a lovely day!