Is marijuana an addictive gateway drug that lowers IQs, triggers psychotic episodes and makes roads less safe?

Or is it a miracle plant that can ease pain or provide a pleasant buzz with health risks on par with forgetting to floss?

Clashing portrayals of cannabis have endured through decades of research and a gradual easing of public resistance to the drug’s use.

Twenty years after California legalized medical marijuana – and as the state embarks on allowing recreational consumption of weed – sorting fact from fiction, anecdotal evidence from rigorous research and “Reefer Madness”-type scare tactics from legitimate health concerns still isn’t easy.

Scientists have been limited in their ability to assess long-term effects of marijuana. That’s largely because the federal government classifies cannabis alongside heroin as a top-tier illegal substance, which among other things means researchers must comply with an ultra-strict set of requirements that they say can prove insurmountable.

Also, as with most drug studies, researchers are forced to rely heavily on self-reported data that are often muddied and can skew results, such as gauging health effects among cannabis consumers who also smoke cigarettes.

“We do need more research,” said Madeline Meier, a psychologist at Arizona State University who’s authored several widely cited studies on marijuana. “Really, in the big scheme of things, this is a new area, an emerging area where we don’t have strong conclusions yet.”

Californians don’t have years to wait for science to catch up with public policy choices.

On Nov. 8, voters decided to legalize recreational pot use in the state under Proposition 64. All residents 21 and over are now free to legally consume cannabis, carry up to an ounce and grow up to six plants per home.

Big players in the medical community were split on the legalization measure.

The California Medical Association, which represents more than 41,000 physicians, was an early supporter of Prop. 64. The group stresses it isn’t encouraging marijuana use. But, it adds, “the most effective way to protect the public health is to tightly control, track and regulate marijuana and to comprehensively research and educate the public on its health impacts, not through ineffective prohibition.”

However, the California Hospital Association, which represents hundreds of hospitals and health care systems, joined law enforcement groups in opposing legalization. In May testimony before a legislative committee, the hospital group’s Connie Delgado expressed concern that emergency room visits and infant exposure to marijuana might increase as they reportedly did in Colorado following legalization.

So how do adults make an informed decision about whether to partake with the science largely unsettled?

On the one hand, research suggests marijuana use poses some potential risks – though largely for vulnerable populations, such as teens and those prone to mental illness.

“There’s no ‘safe’ about it,” Meier said.

On the other hand, there’s growing evidence that the health effects aren’t as severe as many people have believed. And, if precautions are taken – such as limiting access for minors – advocates say many remaining risks are modest and manageable.

In research released earlier this year, Meier used data from a New Zealand study that tracked more than 1,000 people for 20 years to compare the health of cannabis users and nonusers.

“In general,” she said, “people who use marijuana did not show poor physical health by midlife with one exception: They are more likely to have gum disease.”

We’re continuing an occasional series that will survey current research and interview experts on common questions about the health impacts of marijuana use. Here, we tackle the question of addiction.

Q. Is marijuana addictive?

A. For some consumers, yes – but less so than with alcohol.

About 9 percent of people who use marijuana become dependent on it, according to research from the National Institute on Drug Abuse. The study found the dependence rate is about 15 percent for people who drink alcohol, 17 percent for cocaine users and 32 percent for tobacco users.

“Some people can drink normally. Some people can smoke weed normally. But some people can’t,” said Corey Richman, an admissions coordinator at Hope by the Sea drug addiction treatment center in San Juan Capistrano.

Roughly 2 percent of patients at Hope by the Sea are there for marijuana abuse, said Richman, a former addict himself. They’re almost always teenagers brought in by concerned parents, he said.

The earlier young people start using marijuana, the more likely they are to get hooked, with the National Institute on Drug Abuse reporting dependence jumps to 17 percent for teen users.

Stopping heavy marijuana use is often more of a mental struggle than a physical one, said Kevin Alexander, clinical manager at Hoag Hospital’s ASPIRE program in Newport Beach. It can trigger mild withdrawal symptoms similar to quitting tobacco, including irritability and sleep issues. In rare cases, he said, patients experience psychosis.

At the same time, doctors are tapping marijuana’s painkilling benefits to help patients avoid riskier substances such as opioids. A study published in 2014 by the American Medical Association found lower rates of opioid overdoses in states where medical marijuana is legal.

Waiting until at least 18 to start using marijuana lessens the chances of becoming dependent, as does avoiding heavy use of potent pot products, experts say. And people with a family or personal history of addiction might consider avoiding marijuana altogether.

RELATED: Is pot riskier than it use to be? Can it trigger mental health problems? And what about that old Gateway Theory?

Still have questions about potential health impacts of cannabis consumption? Email and we may tackle the topic in a future article.