Steroids should not be used to treat smell loss caused by Covid-19 according to an international group of smell experts, including Prof Carl Philpott from the University of East Anglia.
Smell loss is a prominent symptom of Covid-19, and the pandemic is leaving many people with long-term smell loss.
But a new study published today shows that corticosteroids - a class of drug that lowers inflammation in the body - are not recommended to treat smell loss due to Covid-19.
Instead, the team recommend 'smell training' - a process that involves sniffing at least four different odours twice a day for several months.
Smell loss expert Prof Carl Philpott from UEA's Norwich Medical School, said: "The huge rise in smell loss caused by Covid-19 has created an unprecedented worldwide demand for treatment.
"Around one in five people who experience smell loss as a result of Covid-19 report that their sense of smell has not returned to normal eight weeks after falling ill.
"Corticosteroids are a class of drug that lowers inflammation in the body. Doctors often prescribe them to help treat conditions such as asthma, and they have been considered as a therapeutic option for smell loss caused by Covid-19.
"But they have well-known potential side effects including fluid retention, high blood pressure, and problems with mood swings and behaviour."
The team carried out a systematic evidence-based review to see whether corticosteroids could help people regain their sense of smell.
Prof Philpott said: "What we found that there is very little evidence that corticosteroids will help with smell loss. And because they have well known potential adverse side effects, our advice is that they should not be prescribed as a treatment for post-viral smell loss.
"There might be a case for using oral corticosteroids to eliminate the possibility of another cause for smell loss actually being a confounding factor, for example chronic sinusitis - this is obviously more of a diagnostic role than as a treatment for viral smell loss.
"Luckily most people who experience smell loss as a result of Covid-19 will regain their sense of smell spontaneously. Research shows that 90 per cent of people will have fully recovered their sense of smell after six months.
"But we do know that smell training could be helpful. This involves sniffing at least four different odours twice a day every day for several months. It has emerged as a cheap, simple and side-effect free treatment option for various causes of smell loss, including Covid-19.
"It aims to help recovery based on neuroplasticity - the brain's ability to reorganise itself to compensate for a change or injury," he added.
The research was led by researchers at the Cliniques universitaires Saint-Luc in Brussels (Belgium) in collaboration with the Univeristé catholique de Louvain, Brussels (Belgium), the University of East Anglia (UK), Biruni University, Istanbul (Turkey), Aarhus University (Denmark), Université du Québec à Trois-Rivières (Canada), Geneve University Hospitals (Switzerland), Harvard University (USA), Aristotle University, Thessaloniki (Greece), University of Insubriae (Italy), University of Vienna (Austria), the University of Chicago (USA) and the University of Colorado (USA).
'Systemic corticosteroids in COVID-19 related smell dysfunction: an international view' is published in the journal International Forum of Allergy & Rhinology.