According to the Associated Press 8/24/2022:
About 71,000 people died from overdosing on synthetic opioids like fentanyl in 2021, up from almost 58,000 in 2020, according to the CDC. In comparison, the CDC estimates that in 2020, almost 700,000 people died from heart disease, roughly 600,000 from cancer and around 350,000 due to COVID-19.
Jeff Lancashire is a spokesperson for the CDC’s National Center for Health Statistics. He wrote:
According to preliminary 2021 data, accidents were the leading cause of death among 18-45 year-olds, with accidental synthetic opioid overdoses amounting to less than half of those deaths
The source of the claims regarding fentanyl:
an analysis conducted by the Ohio-based nonprofit Families Against Fentanyl that determined fentanyl was the top killer of people ages 18-45 in 2019 and 2020. The group analyzed publicly available CDC data by comparing synthetic opioid deaths to other causes of death over the last few years, according to spokesperson Moira Muntz.
https://apnews.com/article/fact-check-leading-cause-deaths-fentanyl-154394187670