Billions of euros worth of synthetic drugs were produced in the Netherlands last year, according to a police report published Saturday.

Synthetic drugs with a street value of €18.9 billion ($22 billion) were produced in the country in 2017, according to the report by the Police Academy in the Dutch city of Apeldoorn.

Out of that total, an estimated €3 to €5 billion remained in the hands of Dutch producers, authorities said.

The report underscored that its figures were only estimates, saying that the actual numbers are likely to be much higher.

According to police, the Netherlands is one of the world's largest producer of ecstasy and amphetamines, a type of stimulant drug also known as speed or uppers.

Drugs: Tolerant approach, low penalties

Researchers and authorities attribute the country's position as a top drug producer to a combination of factors, including the Netherlands' tolerant approach towards drug use as well as its relatively low penalties for those caught making the drugs.

The country's good infrastructure and location in Europe also makes it a hub for producing and transporting the illegal substances.

The police report also criticized the government's response to combating illegal drugs, saying that information available on synthetic drugs is "woefully inadequate."

"Anti-drug efforts only receive priority when friendly heads of state (the US, France) raise the alarm about the drug industry in the Netherlands," the report stated, adding that the "effect of this outside pressure is also relatively short-lived."

Dutch Justice Minister Ferdinand Grapperhaus said the police report was "shocking" and said the government plans to invest more money to address "the shameful situation."