If you don't think Americans have a problem with illicit drugs, a new study shows that nearly $150 billion was spent on marijuana, cocaine, heroin, and methamphetamine in 2016.

"To better understand changes in drug use outcomes and the effects of policies, policymakers need to know what is happening in markets for these substances," said study author Greg Midgette. He's an assistant professor at University of Maryland and an adjunct policy researcher at RAND Corp., a nonprofit research organization that funded the study.

From 2006 to 2016, Americans' spending on the four drugs varied between $120 billion and $145 billion a year. In comparison, Americans spent an estimated $158 billion on alcohol in 2017, according to another analysis.

Most of that spending was by a small percentage of people who use drugs every or nearly every day, according to the researchers.

Spending on both illegal and state-licensed marijuana rose about 50% between 2006 and 2016, from $34 billion to $52 billion. From 2010 to 2016, the number of people who used marijuana in the past month increased nearly 30%, from 25 million to 32 million.

Spending on marijuana is about the same as on cocaine and methamphetamine combined.

Heroin use rose about 10% a year between 2010 and 2016, and spending on heroin is now closer to that for marijuana than for the other drugs, according to the study.

Cocaine consumption fell sharply from 2006 to 2010 and continued to fall slowly through 2015, but increased in 2016. In 2015 and 2016, 2.4 million people used cocaine on four more or days in the past month. In 2016, cocaine use increased among a stable number of users as the price per pure gram declined.

Methamphetamine use is difficult to assess due to poor data, according to the researchers.

"While there is considerable uncertainty surrounding national methamphetamine estimates, multiple indicators suggest methamphetamine use has exceeded its previous peak around 2005," said study co-author Beau Kilmer, director of the RAND Drug Policy Research Center.

"While there is much more we can do to reduce opioid use disorders and poisonings involving synthetic opioids, we cannot ignore the growing problems associated with methamphetamine use," Kilmer said in a RAND news release.