Long COVID, also known as post-acute sequelae of SARS-CoV-2 infection or post-acute COVID-19 syndrome, refers to a range of symptoms and complications that persist more than four weeks after diagnosis. Typical symptoms include fatigue, headache, anosmia, ageusia, chronic cough, shortness of breath, impaired concentration and memory (brain fog), sleep disturbances, depression, anxiety, and hair loss. The incidence of long COVID varies according to the data, but it has been reported in approximately 20-60% of acute COVID-19 patients. However, despite its high incidence and significant medical and societal burden, there is currently no clear definition or objective diagnostic criteria for long COVID. Its diagnosis and treatment options are also limited and not established due to insufficient evidence. Nevertheless, a functional medicine approach, especially focused on adrenal functional and adrenal fatigue, can help long COVID patients. Relevant blood tests and urinary organic acid profile can be utilized, and lifestyle modification, oral or intravenous nutrition therapies can be implemented. In this article, we report a clinical case of long COVID with adrenal fatigue, demonstrating significant improvement after functional medical approach and management.