"The numbers are so amazing." Overdose deaths broke a record last year.

A synthetic drug class has replaced heroin on many major drug markets in the United States, ushering in a more deadly phase of the opioid epidemic.

New figures released Thursday by the Centers for Disease Control and Prevention show that drug overdoses killed more than 70,000 Americans in 2017, a record. Overdose deaths are higher than deaths due to HI, car accidents or armed violence at their peak. The data also show that the increase in the number of deaths closely matches the use of synthetic opioids called fentanyls.

Since 2013, the number of overdose deaths associated with fentanyl and similar drugs has increased from 3,000 to more than 28,000. Fentanyl deaths have increased by more than 45% in 2017 alone.

"If we are talking about counting the bodies, where they are and the cause of death, we are talking about a fentanyl crisis," said Jon Zibbell, Senior Public Health Scientist at the RTI International Research Group.

The recent increase in drug overdose deaths has been so severe that it has reduced the country's life expectancy over the last three years, a trend that has not been seen since the Second World War. Life expectancy at birth has decreased by almost four months and drug overdoses are the leading cause of death among adults under 55 years of age.

"The idea that a rich, developed country like ours has a declining life expectancy just does not seem fair," said Robert Anderson, head of mortality statistics at the Cd.C, who helped prepare reports. "If you look at the other rich countries of the world, they do not see the same thing."

In a separate report, the C.D.C. also documented a 3.7% increase in the suicide rate, another continuation of the recent trend. The increases were particularly concentrated in rural areas of America and among middle-aged women, although the suicide rate among men remains higher than that of women at all ages.

Recent measures taken by the federal government to combat the opioid epidemic have focused on opioid prescriptions. But many public health researchers say the rise of fentanyl requires different tools. Opioid prescriptions are falling, even as death rates from overdoses are increasing.

"The number of deaths from fentanyl is up, which is an increase of 45%. it's not a success, "said Dr. Dan Ciccarone, a professor of family and community medicine at the University of California at San Francisco. "We have an epidemic of heroin and synthetic opioids that is out of control and needs to be fought."

Synthetic drugs tend to be more lethal than prescription pills and heroin for two main reasons. They are usually more powerful, which means that small measurement errors can lead to overdose. Synthetic drug mixtures also tend to change frequently, allowing consumers to easily underestimate the strength of the drug they inject. In some parts of the country, the drugs sold as heroin are exclusively fentanyls.

Trends in overdose deaths vary considerably across the country. The epidemic was highest in the northeastern, central-western and central Atlantic states. In the West, where heroin is much less likely to be mixed with fentanyl, overdose rates are much lower. Data from C.D.C. indicate that the overdose trend of a state closely tracks the number of fentanyl deaths.

Despite recent sharp increases in the number of drug-related deaths, some warning signs suggest that 2017 could be the pinnacle of the overdose epidemic. Preliminary C.D.C. the data show that mortality rates have stabilized nationally during the first few months of this year, although there is still a lot of local variation. Several states and cities have embarked on ambitious public health programs aimed at reducing drug-related mortality and bringing more drug users into contact with treatment, and some of these changes could be successful.

"What's encouraging to me is that this is a problem that affects everyone, and we have everyone on the bridge," said Anna Lembke, Associate Professor of Psychiatry at Stanford, and author of a book on how medical practice has contributed to the epidemic of opioids.

But there is still a long way to go. "The plateau concept does not fill me with optimism given the high number of participants," said Joshua Sharfstein, vice-dean of the Johns Hopkins Bloomberg School of Public Health, and former Maryland Hygiene, where overdoses continue to increase. "The numbers are so amazing."