A "true" doctor-assisted suicide can be distinguished from euthanasia in that the patient is actually bringing his or her own life to an end. The doctor in some way facilitates the action, either by providing the means for the suicide, such as in the New England Journal of Medicine article, or by giving the patient some kind of instruction as to the best way of carrying out the act. The difference lies in the fact that it is the patient killing him or herself with the help or advice of a physician, not the physician acting directly to shorten the life of a patient, as in euthanasia. The distinction becomes blurred in reality, however, because often there are no reliable witnesses to the "suicide" to verify that the doctor took no affirmative steps to end the life of the patient. In other instances, the patient may desperately want to kill him or herself but is too weak to do so; thus the doctor actually carries out the life-shortening act. Therefore, any discussion of doctor-assisted suicide must include a discussion of euthanasia, because the two are often indistinguishable.
Note, Has the Time Come for Doctor Death: Should Physician-Assisted Suicide Be Legalized?, 7 J.L. & Health 321 (1992-1993)