The Declaration for Mental Health Treatment (DMHT), an advance directive, is a well-kept secret in Illinois. The DMHT is a specialized document, a sort of niche product among advance directives. Available since 1996, it permits patients to state their wishes in advance about certain forms of mental health treatment if such treatments are recommended and the patient cannot make the necessary decisions. (It should be remembered that mental illness by itself may not render a patient decisionally incapable, although a mentally ill patient may be decisionally incapable from causes other than mental illness.)

In a DMHT the patient gives specific instructions about mental health treatment, and may appoint another person (an attorney-in-fact) to make treatment decisions consistent with the patient's wishes. Specified treatments include psychotropic medications, electroconvulsive therapy, and involuntary commitment to a mental health treatment facility for up to seventeen days. The declaration's authority is limited and need not be followed if an emergency threatens the patient's life or health, or if a court order contradicts the patient's wishes.

Though rarely used, the DMHT is worth knowing about. Its authorizing legislation limits the powers of surrogate decision makers under Illinois' Health Care Surrogate Act. Mental health treatments addressed by the DMHT are specifically excluded from a surrogate's authority. Only a DMHT or Power of Attorney for Health Care can authorize an attorney-in-fact or agent, respectively, to make these treatment decisions. Further, under the Patient Self-Determination Act, a provider's obligation to ask patients if they have advance directives extends to the DMHT. Facility policies on implementing advance directives should include the DMHT. When patients are admitted for mental health treatment, they (or their representatives) should be asked if a DMHT exists. Although newly admitted patients may not be ready to discuss or learn about this directive, caregivers can offer basic education about the DMHT upon discharge. Patients concluding a treatment may welcome the information and find it useful for future reference.