The film coating won't stop the taste as its in your head. (Taken from another forum):
That metallic taste after the ingestion of Immovane or
Zopiclone rather, is normal and, as I understand it, fairly prevalent. What your experiencing is called Dysgeusia and due to the rather complicated neurochemical interface between the taste buds on your tongue and the part of your brain that decides how it feels about what you just put on them, it's not something you can just brush or wash away.
Your tongue is a highly innervated body component and different cranial nerves work in tandem to provide you with the sensation of taste. Different planes of your tongue are also innervated seperately from others and are more sensitive to different chemicals than others. While the tongue is the primary sensor of taste, the whole oral cavity as well as the olfactory system also play a role in the sensation.
While I could not tell you extactly why Immovane causes that unpleasentness and I certainly couldn't tell you what part of the whole taste-brain interface has gone bonkers on you. Nothing in my reference texts reveals the truth of the mystery, though I did check upon reading your post.
SWIM has spoken with patients on Immovane who tried taking cough drops with anesthetic in them and reported that it helped with the taste and made it more pleasent to drink beverages during the hours the bitter taste was present. Benzocaine is often the topical antisthetic used in cough medicine so if you consider trying this method make sure you check the ingredients on the back of the package and make sure you get a flavour that isn't equally as displeasing to you as the Immovane.
Don't forget that your pharmacist is the expert on medication and he or she might be able to make some suggestions to you that your physician may not be able to. Pharmacists know more about medications than the average physician and they might have some tips for dealing with the undesirable side-effects of your medication.
Other patients have also told SWIM that water,
coffee, tea, and juices were particularly bad, but that carbonated beverages were much more pleasant to consume while the taste was still present, though the taste was not completely masked.
Neither of the above suggestions are medically validated of course, but neither are they particularly dangerous, unless you have an allergy to something in the cough medicine.
Dysgeusia will subside as the
drug dissipates in your system, often this is closer to the afternoon on the day after ingesting the medication.