U.S. investment firms have increasingly looked to license marijuana technology from Israel, where a booming cannabis research field has made strides in the past several years, Reuters reported Wednesday. Recreational marijuana is illegal in Israel, and many of the nation's innovations have not been as profitable as their creators had hoped, leading top researchers to look to export their ideas outside the country.

β€œThe main big opportunity in Israel is for [investment] funds to come in here, and get on the ground floor in the scientific research being done. But that is a long-term play, and more capital-intensive,” said Eli Gordis, Israeli founder of private equity firm Alta Fund, Quartz reported earlier in March.

Marijuana is a $15 million to $20 million industry in Israel, where fewer than 25,000 people have medical marijuana licenses. In the U.S., by contrast, the legal marijuana industry is already valued at $5.7 billion and is expected to more than quadruple by 2020, according to Reuters.

What the U.S. lacks, however, is a strong technology or research sector devoted to cannabis. Federally imposed restrictions for researching marijuana in any capacity have hampered studies in the country, and researchers say it is nearly impossible to get a medical marijuana study approved.

β€œIn the United States it's easier to study heroin than marijuana," U.S. psychiatrist Suzanne Sisley, who has studied the use of medical marijuana in people suffering from post-traumatic stress disorder, told Reuters. "With marijuana you have to go through added layers of government red tape," she said, adding, "It highlights the way marijuana research is being shackled by politics."

Medical marijuana is now legal in 23 states and recreational cannabis is legal in four states and Washington, D.C. With legalization in some form being debated in nearly a dozen more states, the legal cannabis industry in the U.S. is set to expand rapidly in the coming decade.