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US life expectancy rose in 2018 for the first time in four years, a welcome reversal for health officials combating a drug epidemic gripping the country.

Deaths from drug overdoses declined for the first time in over 20 years, according to the Centers for Disease Control (CDC).

Overall life expectancy improved by 0.1 years from 2017, to 78 years and seven month, the agency said.

The news was "a real victory", said Alex Azar, the US health secretary.

"It should be a source of encouragement for all Americans who have been committed to connecting people struggling with substance abuse to treatment and recovery," Mr Azar said.

Death rates for unintentional injuries, which includes overdoses, declined by 2.8%, according to the CDC National Center for Health Statistics report, published on Thursday.

Some 400,000 Americans are thought to have died of overdose as a result of the opioid crisis that began in the late 1990s, as painkillers flooded US markets, driving addiction to the drugs.

The brisk rate of mortality due to drug overdose had been cited as key reason for the declining life expectancy seen in previous years.

Deaths from heart disease and cancer, the two leading causes of mortality in the US, continued to decline, falling by 0.8% and 2.2% respectively.

The decline in cancer deaths accounted for 30% of the increase in life expectancy in 2018, the CDC said.

Despite the decrease in overall overdose deaths, however, mortalities due to synthetic opioids- more powerful, related drugs to traditional opioid painkillers - rose by 10%.

Overdose deaths due to synthetic opioids, such as fentanyl, have been on the rise since 1999, and have drastically increased in comparison to other drugs since 2013.

Deaths due to cocaine have tripled since 2012, which Mr Azar called a "disturbing" trend.

The top 10 causes of death - which also includes stroke, diabetes, and suicide - were the same as in 2017, accounting for the majority of deaths.

Suicide rates increased 1.4%, but most of the leading causes saw death rate declines in 2018.

The current life expectancy remains lower than the peak US life expectancy of 78.9 years, from 2014, and is shorter than the average of 80 years in the OECD, an organisation of mostly rich countries.

Experts cautioned that an increase in a single year may not indicate a trend - and the US remains in last place among wealthy nations for life expectancy.