For the study, researchers from the University of Oxford in the UK looked at 14 neurological and mental health disorders in 2,36,379 Covid-19 patients mostly from the US.
The findings showed 34 per cent were diagnosed with a neurological or psychiatric condition within six months of infection.
The most common condition was anxiety (17 per cent) and mood disorders (14 per cent).
Neurological diagnoses such as stroke and dementia were rarer, but people among admitted to intensive care, 7 per cent had a stroke and almost 2 per cent were diagnosed with dementia.
"These are real-world data from a large number of patients. They confirm the high rates of psychiatric diagnoses after Covid-19, and show that serious disorders affecting the nervous system (such as stroke and dementia) occur too. While the latter are much rarer, they are significant, especially in those who had severe Covid-19," said lead author Paul Harrison, Professor at the University of Oxford.
"Although the individual risks for most disorders are small, the effect across the whole population may be substantial for health and social care systems due to the scale of the pandemic and that many of these conditions are chronic.
"As a result, health care systems need to be resourced to deal with the anticipated need, both within primary and secondary care services," Harrkson said.
The study also found 44 per cent greater risk of neurological and mental health diagnoses after Covid-19 than after flu, and a 16 per cent greater risk after Covid-19 than with respiratory tract infections.
This shows that Covid-19 does lead to a greater risk of neurological and psychiatric disorders than these other health conditions, the researchers said.
However, there was no clear evidence that Covid-19 led to an increased risk of Parkinson's or and Guillain-Barre syndrome.
"Our results indicate that brain diseases and psychiatric disorders are more common after Covid-19 than after flu or other respiratory infections, even when patients are matched for other risk factors. We now need to see what happens beyond six months," said co-author Max Taquet, from the University of Oxford.