Life expectancy for Americans dropped once again in 2017, as the rates of fatal opioid overdoses and suicides continued to climb.

An American born in 2017 is expected to live to be 78.6 years old, according to data from the CDC's National Center for Health Statistics. That's one-tenth of a year lower than the previous year, or, put another way, it shaves 1.2 months off the life expectancy of a baby born in 2016. Life expectancy dropped from 2014 to 2015, then held steady in 2016, the CDC said.

The decline is a troubling sign for the United States, which already usually ranks lowest among other wealthy countries for life expectancy.

The top three causes of death, unchanged from previous years, were heart disease, cancer and unintentional injuries. The report attributed the drop in life expectancy to increases in mortality from unintentional injuries, which includes most fatal drug overdoses, among other factors.

Last year, there were 70,237 deaths attributed to drug overdoses in the United States. Adjusting for age, the rate of drug overdose deaths increased by 9.6 percent from the previous year. However, the rate of overdose deaths is not increasing as fast as previously; in 2016, the rate rose by 21 percent.

West Virginia, Ohio and Pennsylvania had the three highest age-adjusted rates of fatal overdoses.

The rate of overdose deaths involving synthetic opioids other than methadone increased by 45 percent from the previous year. According to the CDC, fentanyl, one such synthetic opiate, is 50 to 100 times more potent than morphine and often mixed with heroin or cocaine, sometimes without the user's knowledge. Since 2013, the number of deaths from overdoses involving synthetic opioids have jumped sharply.

First lady Melania Trump called the opioid epidemic the "worst drug crisis in American history" in a speech Wednesday. Advocacy about the crisis and its effects on children are a part of her "Be Best" campaign, which focuses on childhood well-being.

"The pattern of drugs involved in overdose deaths has changed in recent years," the NCHS report said, noting that the rates of overdose deaths involving heroin, methadone, and natural and semisynthetic opiates — oxycodone, for example — were unchanged from 2016 to 2017.

The majority of drug overdose deaths were unintentional, according to the NCHS report. Seven percent of those deaths were determined to be suicides. (The data are compiled using information from death certificates, which list an official cause of death.)

Suicides overall were up by 3.7 percent in 2017. Since 1999, the national suicide rate has increased by 33 percent. The country's most rural counties had suicide rates almost twice as high as those for the most urban counties.

The increase in suicides did not affect its spot as the 10th leading cause of death in the United States for the 10th year in a row, but the NCHS report did list it as another reason for the decline in life expectancy.

WATCH: These party drugs could become the answer for clinically depressed patients