Universal Declaration of Human Rights - Article 5 :

« No one shall be subjected to torture or to cruel, inhuman, or degrading treatment. »
 

UN Declaration on the Protection of All Persons Subjected to any Form of
Detention or Imprisonment Against Torture and Other Cruel, Inhuman or
Degrading Treatment or Punishment - Article 1 :

« For the purpose of this Declaration, torture means any act by wich severe pain or suffering, wether physical or mental, is intentionelly inflicted by or at the instigation of a public official on a person for such purpose as obtaining from him or a third person information or confession, punishing him for an act he has commited or is suspected of having committed, or intimidating him or other person. »
 

UN Standard Minimun Rules for the Treatment of Prisoners - Article 22(2) :

« Sick  prisoners who require specialist treatment shall be transfered to specialized institutions or to civil hospitals. »
 

UN Principles for the Protection of Persons with Mental Illness and for the
Improvement of Mental Health Care :

Principle 1 :

1. « All persons have the right to the best available mental health care, which shall be part of the health and social care system. »

2. « All persons with a mental illness, or who are being treated as such persons, shall be treated with humanity and respect for the inherent dignity of the human person. »

3. « All persons with a mental illness, or who are being treated as such persons, have the right to protection from economic, sexual and other forms of exploitation, physical or other abuse and degrading  treatment. »

Principle 20 :

2. « All persons [serving sentences of imprisonment for criminal offences, (...) and who are determined to have a mental illness] should receive the best available mental health care as provided in principle 1 above. »
 

UN Principles of Medical Ethics (relevant to the role of health personnel,
particularly physicians, in the protection of prisoners and detainees
against torture and other cruel, inhuman or degrading treatment or
punishment) - Principle 1 :

 « Health personnel, particularly physicians, charged with the
medical care of prisoners and detainees, have a duty to provide them with
protection of their physical and mental health and treatment of disease of
the same quality and standard as is afforded to those who are not in prison
or detained. »