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.
The University of East Anglia is conducting a 12-week trial.
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.
Lina Alnadi, 29, from London, developed parosmia after Covid, which means the odour of many common things has changed for her.
Tap water, for example, smells horrendous, the odour you or I might get from a swamp or sewer.
The herb coriander has the whiff of deodorant.
And eggs - one of Lina's favourite foods - smell like burnt rubber.
"You take your sense of smell for granted," she says.
"Losing it was devastating. It affected my diet dramatically.
"There were lots of foods I just couldn't face eating. It was really upsetting."
Life hacks
Simple things such as showering or brushing her teeth are also unpleasant because of her skewed sense of smell.
But the situation has improved gradually and Lina has found a few life hacks that help.
"Adding lemon or chilli to foods can make them smell better," she says.
"I also experimented and made lists of safe foods that would not make me want to vomit.
"I had to be creative about it to make sure I was eating enough of the right things to stay well."
Olfactory bulb
Lead researcher Prof Carl Philpott, from UEA's Norwich Medical School and James Paget University Hospitals NHS Trust, said: "We want to find out whether there is an increase in the size and activity of damaged smell pathways in patients' brains when they are treated with vitamin-A nasal drops.
"We will look for changes in the size of the olfactory bulb - an area above the nose where the smell nerves join together and connect to the brain.
"We will also look at activity in areas of the brain linked to recognising smells."
Vitamin A, or retinol, helps maintain:
- *the immune system - the body's defence against illness and infection
- *eyesight, particularly vision in dim light
- *the skin and lining of some parts of the body, including the nose
Many dairy foods, as well as some vegetables, contain this fat-soluble vitamin.
But people taking vitamin-A supplements should be aware too much can be harmful.