In relation to the Doctrine of Double Effect, a literal follower of Natural Law would not allow euthanasia. This is because the Doctrine does not allow a bad act even if it results in a good consequence. People may argue that to assist someone in killing themselves is a bad act that results in the good consequence of that person being relieved of their pain and this would therefore be wrong according to the Doctrine. However, if we accept that death can sometimes be a by-product of another action, then euthanasia may be acceptable even when applying the Doctrine of Double Effect. For instance, if someone commits euthanasia with the primary intention of relieving pain, but the secondary effect of this is that they die, some people would argue that this complies with the Doctrine because it is a good act with a bad consequence. For example, Doctor Kevorkian helped Thomas Hyde to commit suicide in 1993. Although Doctor Kevorkian knew this was an illegal act, he justified himself by saying that his primary intention was only ever to relieve pain but that an unfortunate secondary side effect of this was death. In this way, a follower of Natural Law might accept euthanasia because it can be applied to the Doctrine of Double Effect.
However, according to Natural Law, there are interior and exterior acts. The interior act (the intention) and the exterior act (the action) are both of equal importance, according to Aquinas, and as a result, both must be good to result in a good act. This means that followers of Natural Law may not agree with any forms of euthanasia because even if the intention is good e.g. relieving pain, the act of assisting in someone’s suicide, either actively or passively is wrong. On the other hand, followers of Natural Law may accept passive euthanasia but not active euthanasia based on the Doctrine of Double Effect. Active euthanasia involves doing something deliberate that leads to someone’s death which is a bad act, possibly leading to a good consequence, whereas, passive euthanasia occurs when the patient dies because the medical professionals either do not do something necessary to keep the patient alive, or when they stop doing something that is keeping the patient alive e.g. not performing a life-extending operation. In this case, the good act is saving the patient the stress and pain of having to undergo surgery with the bad consequence being that they might die sooner than they would have done had the operation been performed.
Furthermore, some people distinguish between human beings and personhood. A human being is purely a body and has no characteristics, whereas personhood refers to the person as a whole including their characteristics, although philosophers debate as to which characteristics are distinguishing of personhood. For example, John Locke says that to be a person, one needs to have ‘the ability to think and reflect’ whereas Joseph Fletcher states that personhood consists of self-awareness, self-control, sense of the future, sense of the past, capacity to relate to others, concern for others, communication and curiosity. Some people think that a person is always a person, even if they lose what these philosophers believe to be defining characteristics of personhood, and therefore would never allow euthanasia because a person has sanctity of life. Conversely, other people suggest that there is a difference between a human being and a person and to be a person, someone needs to possess specific characteristics. Someone terminally ill may lose the defining characteristics of personhood and as a result, some people may see them as a human without personhood. In this instance, Aquinas may have viewed some terminally ill people who did not possess these characteristics as having a vegetative soul due to his belief of ensoulment and some people would use this to argue that some terminally ill cannot be classed as full people anymore, so therefore have the right to die. As vegetable souls do not have sanctity of life, it can be argued that euthanasia would be acceptable according to Natural Law. However, the characteristics that people are said to need to possess in order to be a person are not always possessed by children and therefore some people see it as acceptable to commit infanticide in view of these traits. Most people would consider infanticide to be a barbaric practise and think that although children may not yet possess these traits they have the potential to in the future. This causes us to question if euthanasia is not also a barbaric practise and if someone is in a coma, they also have the potential to develop these traits one day too. This leads many Natural Law followers to accept euthanasia on the basis that some humans do not have personhood, but reject euthanasia if the human has the potential to develop personhood e.g. if a person is in a coma.
Although manipulation of Natural Law means there are times in which euthanasia could be acceptable, most people would generally accept that Natural Law would never justify euthanasia due to the five Primary Precepts which are clearly opposed to it.