"There is a big mountain of this stuff. A lot of it," Fredrik Støtvik from the Norwegian Customs Association told The Local. "And we know that we're just catching a fraction of it, so we need more staff to take care of it."
Synthetic cannabis is made by spraying a legal herbal smoking mix with synthetic cannabinoids that act on the brain in a similar way to THC, the main active ingredient in cannabis.
"The problem is that synthetic cannabis is very much more dangerous than ordinary cannabis," Støtvik said. "You never know what's in it."
He said that young Norwegians were buying the drug on internet sites such as Silk Road, the website shut down by the FBI at the start of October, and then had it posted directly to their houses.
"They just order it over the internet, and they will get it in their mailbox, so that's the challenge for us, because we don't have so many officers," Støtvik said. "We have officers who work in the post office, but there's a lot of post."
Norway introduced new laws in 2011 which would make synthetic cannabis illegal even if the specific compounds included in it were not on the list of banned drugs, but Støtvik said keeping up with synthetic cannabis producers remained a problem. In 2009, synthetic cannabis was banned in the UK, Sweden and Germany.
"When we have seizures we can see that there's a lot more now than there was earlier. These kinds of drugs are quite new, and the problem is that the producers are always ahead of us. They produce something new and then we have to try to develop the skills to stop them."
The customs association has asked to meet Norway's finance minister Siv Jensen to petition for increased funding.