Well it depends on who is giving it and how much they know about the drug. When it's drugs like morphine that medical people give to lessen a patient's pain, it needs to be administered skillfully, otherwise it could overpower the person's awareness. So I think it has to be used wisely and by someone who is a professional and knows how to use it because when we're dying it is an opportunity. According to Buddhism, if we overpower our awareness at that time, it might lessen our opportunities to die skillfully. If we are overpowered by drugs at that time, then we may not be able to die in a beneficial way. Sure, if a person has a lot of pain it's very helpful to lessen their pain, so that they can direct their mind to something else rather than just the pain. So it has to be done skillfully, I think, and by someone who knows what they are doing, so that it is not overdone.
I heard of a person who had a lot of pain, who was terminally ill and they were having a lot of problems with dealing with pain, and in fact they were angry much of the time. It so happened that they were also being helped by a meditation teacher to learn how to deal with the pain. One night, they got a bit of a break through, they did a bit of a universalizing type of reflection and they opened up to the universality of suffering. A great wave of compassion arose for themselves and all beings at that time and their personality changed over night. They changed from someone that the nurses didn't want to go to be near to becoming a favorite patient on the ward. So it is an opportunity at times, if a person knows how to deal with their pain, rather than just dull it, to increase the level of our pain threshold and learn ways to use it to develop the mind.