As the level of recreational marijuana use rises in Maryland, mental health experts say so does their level of concern.

Could there be more people suffering psychosis in the short term and schizophrenia in the long term? Will more people feel suicidal? Could short-lived relief from anxiety and insomnia turn to dread?

Researchers and clinicians don’t fully know what to expect because studies of the plant the federal government still considers illegal have been less than robust.

“I feel like we’re flying blind because the science is way behind where the marketplace is,” said Johannes Thrul, a substance use researcher in the Johns Hopkins Bloomberg School of Public Health.

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“One area where the science is pretty clear, and at times gets ignored by enthusiasts, is that it’s addictive,” he said of marijuana, which became legal for recreational use in Maryland this month. “Over the long term, heavy use is probably not a good idea.”

While marijuana, also known as cannabis, isn’t as deadly a threat as opioids, and there is evidence of medical benefits for certain conditions like nerve pain, seizures and appetite loss, experts do not consider it risk-free — and many consider it a particular threat to those already with mental health disorders or at risk for one.

It’s just less clear exactly who will be heavily affected and when. Researchers expect to answer some of those questions about negative effects on mental health, as well as potential medical benefits, as more studies are begun.

Who’s most at risk for marijuana-related mental health problems?

Thrul and others say there are likely several factors at play, including marijuana potency, frequency of use and even if the cannabis is smoked, vaped or eaten.

Age seems to be a factor, with teens and young adults more likely to have psychotic episodes after using marijuana — that could manifest as auditory hallucinations, like hearing voices, paranoia, uneasiness with others and delusional thinking. That’s especially likely for those with a genetic predisposition for mental illness or people who have suffered trauma.

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A Danish study published earlier this year found that longer-term use is linked to schizophrenia, particularly in males up to age 26. Maryland’s recreational marijuana law forbids anyone under age 21 from buying, using or possessing the drug. The National Institutes of Health suggests long-term use spans 12 months.

But using too much at once can can be a problem for anyone, said Dr. Nora D. Volkow, director of the NIH’s National Institute on Drug Abuse.

“There are gaps in our knowledge for sure,” she said. “But if the THC in marijuana is a sufficiently high dose, we know it can make someone experience psychotic behaviors — hallucinations, paranoia.”

THC, or tetrahydrocannabinol, is the major psychoactive component in cannabis among the more than 400 chemicals comprising the plant.

How long the psychological damage lasts beyond intoxication and other conditions people are at risk for is the part that’s unsettled, Volkow said.

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She believes the majority recover. But she added if a lot more people are using highly potent cannabis regularly now that it’s recreationally available in about half the states, the country could still see significant issues down the road.

When does marijuana use become a problem?

Recent data from NIH suggest that about 30% of those using cannabis may have some degree of marijuana use disorder, meaning they are unable to stop using and could eventually experience health or social issues.

The number could rise with availability and the dramatic shift in public opinion about marijuana. A recent Pew Research Center survey found about 46% of Americans have tried the drug, and nearly 9 in 10 people believe it should be legal for medical or recreational use. Mostly that’s because people see medical benefits or think law enforcement should focus on other crime.

The support belies the concerns of some mental health care providers, who expect an uptick in patients who need immediate psychiatric treatment.

“Everyone that actually treats patients tends to be on board that this [increase in use] is a problem,” said Dr. Paul Nestadt, clinical director of the Jack and Mary McGlasson Anxiety Disorders Clinic at Johns Hopkins.

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When he’s not directing the anxiety disorders clinic or teaching in Hopkins’ School of Medicine, Nestadt treats patients struggling with disordered substance use and in acute psychiatric distress at Johns Hopkins’ Dual Diagnosis Inpatient Unit — where cannabis comes up frequently, he said.

He said he recently treated one woman diagnosed with schizoaffective disorder, a psychiatric condition characterized by symptoms of psychosis, such as hallucinations or delusions, and bipolar or major depressive disorder.

Prescription medication helped manage her symptoms, Nestadt said. But during multiple stays in the intensive care unit, Nestadt said the patient, who was also registered to buy medical cannabis in Maryland, told providers she had smoked cannabis prior to “serious suicide attempts.”

“She’s like, ‘No, you don’t get it. This is the only thing that helps my anxiety,’” Nestadt said. “Just like taking a shot of tequila will help your anxiety, but it’s not good in the long term.”

Nestadt said he attempted to reach the medical provider who cleared his patient to buy cannabis at Maryland dispensaries for months, intending to ask the provider to revoke the patient’s medical cannabis card. With no response, he emailed an official from the then-Maryland Medical Cannabis Commission (since renamed to the Maryland Cannabis Commission).

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Nestadt said the state regulator would not intervene, citing patient privacy requirements.

“There are some medical uses for cannabis, but certainly not psychiatric ones,” Nestadt said.

Still, he said it’s not unusual for his psychiatric patients to say they’ve been told cannabis is a treatment. Telling them otherwise is “a complicated message to send.”

Who should avoid using cannabis?

The clinicians and researchers say those diagnosed or at risk for conditions such as depression, anxiety, sleep disorders, or vulnerable from traumas, should avoid using cannabis. Research going back years also suggests it’s possible for some chronic users with no family history of psychotic illness to develop lasting symptoms of schizophrenia. People may feel better initially but symptoms can worsen over time as tolerance and dosing rise.

Some experts also advised healthy people using cannabis to consume smaller amounts first. People react to

edibles, like marijuana-infused gummy bears or baked goods, more slowly than those who smoke because it takes more time to get into the bloodstream. They say start with small amounts and wait an hour before consuming more.

As for those medical benefits, there is most evidence for relief from nerve pain, glaucoma, seizures and wasting disorders associated with chemotherapy — conditions approved under Maryland’s medical cannabis law.

Post-traumatic stress disorder, or PTSD, is also a medically approved use in the state, and being eyed by veterans groups, among others. But officials say more research is needed on long-term effects.

Groups including the American Psychological Association supported federal legislation to make it easier to study cannabis so the scientific community can learn more definitively about harmful and therapeutic effects.

For now, the American Psychiatric Association opposes cannabis as medicine, citing “no current scientific evidence” it’s beneficial for the treatment of any psychiatric disorder, and there is “strong association of cannabis use with the onset of psychiatric disorders.”

Since cannabis use disorders seem more common in younger people, Volkow said researchers at NIH already are studying marijuana’s effects through the Adolescent Brain Cognitive Development (ABCD) Study.

The research launched in 2015 and follows development of thousands of 9- and 10-year-old children. The children should just be coming upon the age when some are likely to be exposed to marijuana, and researchers will see how it affects them.

“Some people smoke all their life and never see effects. Some have short exposures and have severe experiences. We’re all different with different vulnerabilities and resilience,” Volkow said. “We’ll see if this leads to changes and in whose brains.”