US President Donald Trump has declared the country's opioid crisis a "public health emergency", but stopped short of issuing an order that would allocate more federal funds to address the epidemic.

Opioids are a type of drugs that include illegal substances, such as heroin, and legal painkillers - medications such as oxycodone, codeine and morphine are all types of opioids.

"Effective today, my administration is officially declaring the opioid crisis a national public health emergency under federal law," Trump said during a speech addressing the issue on Thursday.

"I am directing all executive agencies to use every appropriate emergency authority to fight the opioid crisis," he said.

"We can be the generation that ends the opioid epidemic."

According to the latest figures from the Center for Disease Control and Prevention (CDC), deaths from opioid overdoses - either prescription or illegal - have quadrupled in the US since 1999.

The CDC recorded 33,091 deaths in 2015.

Since 2000, more than 200,000 Americans have died from overdoses of prescription opioids.

Redirecting funds

Trump has been under increased pressure from those on both sides of the political spectrum to fulfil his campaign promise to do more to address the opioid epidemic.

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In August, the president said he would declare the crisis a "national emergency", but on Thursday backtracked on that promise, instead calling the crisis a "public health emergency".

The difference between the two has to do with how and what funds can be used.

Had the president declared a "national emergency" under the Stafford Act, agencies would have gained access to additional funds via the Federal Emergency Management Agency's Disaster Relief Fund, which is typically used in cases of natural disasters like Hurricanes Maria and Irma.

Instead, Trump chose to direct the Department of Health and Human Services to declare the crisis a "public health emergency", which only reallocates already-existing grant money and eases certain policies to help combat the problem. It also expires after 90 days, but White House officials have reportedly said this could be easily renewed.

According to local media, the effort will initially be funded through the Public Health Emergency budget, which contains less than $60,000.

Trump issued an executive order in March that set up a commission to examine the national response and make recommendations about how to tackle the issue.

In July, the committee said that the administration should "declare a national emergency under either the Public Health Service Act or the Stafford Act".

Trump said he expects to receive the final report from the commission next week and will begin implementing its recommendations as soon as possible.

'Weak and insufficient'

Al Jazeera's Kimberly Halkett, reporting from the White House, said that some in the US consider Thursday's announcement a "good first step".

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"But at the same time there is a little bit of disappointment, and even some criticism because of what this doesn't include - extra funding that would have come with the national emergency declaration," she added.

A number of Democrats called Trump's announcement on Thursday "weak" and "insufficient".

"While the steps outlined by the president may be helpful in some instances, without robust and dedicated funding, health care providers, treatment facilities and others working on this multi-faceted crisis will be hamstrung in their efforts to protect American communities from the scourge of opioid addiction," Congresswomen Rose DeLauro and Nita Lowey said in a statement.

"Further, mere shifting of already insufficient resources threatens to hamper critical investments in other forms of health research and treatment," the legislators added.

Trump outlined a number of ways the administration will seek to combat the crisis, including working with health professionals across the board, as well as drug enforcement agencies.

According to US media, the administration is expected to work with Congress to set up additional funds to help address the crisis during the end of the year budget negotiations.