That is probably because these patients were on a narcotic for pain. They may be considered as alternatives to other antinausea drugs. Some in this group of drugs could effect the availability of dopamine and should be avoided, if possible. Dopamine ant agonists decrease dopamine. There are other treatments for PMS available which might be considered first.
Neuroleptics are dopamine ant agonist.
These drugs should not be stopped without medical advice. This might also hold true for any drug that contains levodopa. The body must use iron to replace lost blood and make new red blood cells thus potentially lowering the patient's ferritin level. See C of this Section for more information. They act by blocking dopamine receptors.