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From: Brian Symonds <[log in to unmask]> Hi Bill and Amy You were wondering if it was reasonable for your friend to be taking Apo-Morphine and Domperidone (Motilium) at the same time, wondering if the Domperidone would block the action of the Apo-Morphine. Following is my understanding of these drugs. There may be someone on the list who has more information. It is true that Domeridone is a dopamine antagonist, and works by blocking dopamine receptors. However, because of its structure, it does not pass into the brain tissue from the blood stream very easily, and thus acts outside of the central brain tissue. Since the brain cells (chemoreceptor cells) that can cause nausea and vomiting when irritated by Apo-Morphine or dopamine are not in the central brain tissue, but rather outside of it, Domperidone will act on them and help to prevent the nausea and vomiting caused by Apo-Morphine and dopamine without going into the central brain tissue to block the effects of these drugs in helping with Parkinson's Disease. Additionally some people think that L-dopa and Apo-morphine have a direct chemical irritant effect on the stomache which can cause nausea and vomiting, and Domperidone will also help to block this effect. Having said that Domperidone does not cross the blood-brain barrier into the central brain tissue, nothing is perfect, and Domperidone does do this to a small extent. There are thus a small number of people (supposedly less than 1% who take the drug) who get central brain tissue side effects from this drug such as dry mouth, insomnia, nervousness, irritability, and tremor. These symptoms go away when the drug is stopped. Domperidone may be better than Cisapride (Prepulsid or Propulsid) at controlling the nausea and vomiting caused by drugs used to treat Parkinson's.