Smoking marijuana is tied to less motivation at work, a new study finding suggests.

The author of the study said it can’t prove whether that’s due to the drug’s effects, the social environment in which it’s used or whether pot smokers are just more likely to be laid-back from the get-go.

Christer Hyggen, researcher at the Oslo-based social research institute NOVA, suspects pot is the culprit, another possible explanation is that people who aren’t so happy with their work situation or motivated on the job are more likely turn to drugs.

“There’s a popular belief that people who smoke cannabis are slackers and that they don’t want to work,” Christer Hyggen told Reuters Health.

To see how well that perception held up, Christer Hyggen analyzed data from a 25-year-long study of close to 1,500 Norwegians. Starting in 1987, when they were in their late teens and early 20’s, participants filled out surveys that included questions on their recent pot use on five different occasions, into their 40’s.

They also rated their attitudes on statements that reflected work commitment, such as “It is very important for me to have a job” and “I feel restless when I have no work to do”, ranked on a scale of 1 to 5, with 5 reflecting the most commitment.

Smoking marijuana is tied to less motivation at work, a new study finding suggests

People who reported smoking in the past year generally reported less dedication to work than abstainers, according to findings published in the journal Addiction.

The pattern held after Christer Hyggen took into account their mental health, satisfaction with their work environment, their economic background and how much alcohol they drank.

Christer Hyggen also found that those who only reported recent smoking on one survey – “the experimenters” – tended to be as committed as abstainers as they got older. That wasn’t the case for participants who repeatedly acknowledged marijuana use: their work commitment continued to decline into adulthood, and remained significantly below that of never-smokers.

By the last survey, in 2010, the 63 repeat users had an average score of 3.9 on questions of work commitment. That compared to scores between 4.2 and 4.3 in participants who had only experimented with marijuana or never tried it, including those who said their friends used the drug but they didn’t.

The findings suggested that over time “people who quit smoking cannabis increase their work commitment and people who take up smoking cannabis reduce their work commitment”.

While the results can’t prove a cause-and-effect relationship, “we were able to at least close in on this association”.

Such a link fits logically, according to another researcher not involved in the study.

“For adolescents who are engaged in marijuana use and substance use, to the extent that that decreases or limits the academic achievement they would have achieved otherwise, that would limit their employment opportunities,” said Kimberly Henry, from Colorado State University in Fort Collins, who has studied marijuana and truancy in adolescents.

“I think like many of these kinds of behaviors, there is kind of a spiral cycle where one reinforces the other,” she said.

Christer Hyggen said that it’s not a bad idea to stay away from drugs including marijuana.

“At the same time I don’t think we should be overly afraid of people experimenting with drugs in youth,” he said, as young people with that type of marijuana use didn’t end up with a diminished work ethic as adults.

Kimberly Henry agreed that heavier marijuana use is what’s worrisome when it comes to school and work performance.

“This idea that makes sense from theory and just conventional wisdom is that it’s the higher-level use that’s probably causing the most problems,” she said.