Using hashish oil to soften the hair

If the oil is derived from the hashish which
intoxicates and which is not allowed to be sold because it contains
 forbidden intoxicating substances, it is not permissible to use
it. Allaah does not put the cure of the ummah of Muhammad in something
that He has forbidden for them. If the hashish in question is the hashish
which causes intoxication and is classed as a drug, then it is not permissible
to use it and treat disease with it. These drugs are harmful and are
themselves a disease. It was narrated from Umm Salamah that the Prophet
(peace and blessings of Allaah
be upon him) said: “Allaah does not put the cure for my ummah in something
that He has forbidden to them.” And Allaah knows best.