Someone who is not feeling well and strong smells (like that of an cut onion or strong fragrances, etc) is somewhat of a rafuah for this person, may they smell these things on Shabbos? (i.e. is there a problem of refuah be-Shabbos when it comes to re’ach?)
If the specific item that it being smelt is used only as a refu’ah (medicinal treatment), it is forbidden to smell on Shabbos.
However, if the item is also used for smelling by healthy people, such as “tabac,” it is permitted to smell, even if one’s intention is for the purpose of refuah.
It is permitted to smell Vicks or other ointments (such as eucalyptus oil) for the purpose of clearing an airway. This is not considered healing.
For Vicks, see Be’er Moshe, Vol. 1, no. 34, sec. 12 (permitting).
For smelling “tabac,” see Be’er Heitev 328:30 and Sha’arei Teshuvah 328:1 (both permitting).