Introduction: There has been little consensus for a specific definition of long COVID, though several organizations have created varying ones. We sought to examine the definition of long COVID used in ongoing clinical trials.

Methods: We searched 'long COVID' and related terms on both PubMed and clinicaltrials.gov for randomized studies that either included patients with long COVID or had a persistent or long-term COVID-related outcome and abstracted long COVID definition components.

Results: Of the 92 studies, a laboratory-only confirmed diagnosis of COVID-19 was stipulated in 54.3% (n = 50) studies. We found eight different time durations specified for how long symptoms needed to have occurred, ranging from 4 to 52 weeks, with 12 weeks being the most common (34.8%; n = 32). 35.9% (n = 33) did not specify a time duration. There were 57 different symptoms specified in total, with a median of one symptom identified per study (range 0-32). 8.7% of trials adhered to NICE or WHO definitions.

Conclusion: Standardized definitions of long COVID should be applied in studies assessing this condition to unify and harmonize research on this topic.