Vitamin A nasal drops might be able to treat the loss or altered sense of smell in some people who have had Covid, UK researchers say.
Only some of the volunteer patients will receive the treatment but all will be asked to sniff powerful odours such as rotten eggs and roses.
And brain scans will check if the vitamin has repaired injured olfactory pathways or "smell nerves".
Loss or altered sense of smell is a common symptom of Covid, although many other viruses, such as flu, can also cause it.
And while most people naturally regain it within a couple of weeks, many have been left with continuing smell disorders.