I'm a doctor and planning to take psychiatry as my profession. In psychiatry we give sleeping pills for insomnia and anti-anxiety. These drugs are in the benzodizepines family which cause sleepiness and calms the patient and relieves his anxiety. In large doses they may cause amnesia and forgetfulness. Is the use of these drugs permissible in Islam if we don't have any alternative to them? Please do answer my question, as I have to decide taking psychiatry as a profession.

Praise be to Allah, the Lord of the World; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

Studying psychiatry, as a specialization is permissible provided the doctor does not use any Haram material in treating his patients. He should try to guide his patients to the remembrance of Allah, recitation of the Qur'an performing obligations and avoiding prohibitions. He has to inform them that the happiness in this life and in the next life is only in following the Orders of Allah and all the miseries are in deviating from the Path of Allah.
As for the medicine you are enquiring about, it is permissible if there is no alternative provided no more than the required quantity is prescribed. Over dosing may severely harm the mind of a person, while keeping and protecting one's mind is very important in Sharia.
Allah knows best.