All users of mental health services should be given a written individualised treatment plan, the Amnesty report says.
The report also criticises the fact that there is an over-reliance on medication alone as treatment for many serious mental illnesses.
The report says that patient participation in treatment plans is limited, and many patients complain they rarely have their treatment discussed with them.
This, states the report, "prejudices the right to informed consent to treatment".
In addition, Amnesty says there is a need for a "comprehensive system of personal advocacy to assist some people with mental illness, particularly while seriously ill".
Referring to the UN Principles for the Protection of Persons with Mental Illness, one of which underlines an individual's right to "the least restrictive or intrusive treatment", the report says there appears to be an over-reliance on medication alone as therapy for many serious mental illnesses.
Amnesty calls on the Government to publish standards and guidelines in relation to the prescribing of medication.