Answer
(Fatwa: 99/94=B)
It is makrooh–e-Tahreemi (undesirable to an extent of haram) to consume charas (hashish) if it is used in a quantity which does not intoxicate, otherwise taking it in an intoxicating quantity is unlawful and haram. Moreover, it causes resemblance with the people of Hell since they will also discharge smoke from their mouth, thus it is disliked by Allah. As far as the matter of hashish helps to concentrate more on studies is concerned, it is your baseless obsession.
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband