Marijuana gives people with schizophrenia a quick rush but worsens their psychotic symptoms within a few hours, a new study reveals.

Researchers in the Netherlands recruited 48 psychiatric patients and 47 healthy people to record what they were doing and how they felt 12 times a day for six days. All the study participants were regular pot smokers. The results showed that schizophrenia sufferers were more sensitive than healthy individuals to both the positive and negative effects of marijuana, or cannabis.

"People feel better when they use cannabis, and that's logical, because otherwise they wouldn't use cannabis," said study researcher Cecile Henquet of Maastricht University Medical Center in the Netherlands. "In spite of that, in the long run it's not so good for their psychotic symptoms."

Researchers have long wondered whether the mentally ill are using reefer to alleviate the classic symptoms of the disease: delusions, hallucinations and jumbled thoughts.

The new studies turn that reasoning on its head, said Deepak Cyril D'Souza, a psychiatrist at Yale University who was not involved in the study. "What the data clearly show are that, if anything, the core symptoms of schizophrenia actually get worse after using cannabis," he said.

The results, published in the June issue of the British Journal of Psychiatry, help explain previous findings that people with schizophrenia who smoke marijuana require more hospitalization, respond less well to medication and have more trouble with memory tests.

Henquet said therapists have these facts in mind when they advise their mentally ill patients not to get high. Instead, she said, therapists may need to explore the positive effects with their patients and then get them to acknowledge the downside.

D'Souza said schizophrenics don't anticipate that after the positive effects of getting high wear off, their hallucinations get worse. "Showing people with schizophrenia this pattern might help them think about [the risks of] using cannabis," he said.

The new study is further evidence of the tangled relationship between marijuana and schizophrenia. Researchers know that getting high can trigger schizophrenic symptoms in people who are at risk for mental illness.

The culprit is most likely the signature ingredient of pot, the chemical delta-9 tetrahydrocannabinol, or THC. In laboratory studies, people who ingest THC experience psychotic symptoms.

According to one estimate, if marijuana use were eliminated in the U.K., where the THC content of the drug is reportedly very high, the rate of schizophrenia would decrease by 8 percent to 14 percent.

Henquet said it's likely that marijuana triggers schizophrenic symptoms in people who have genetic mutations that sensitize them to the drug's psychotic effects.

Oddly enough, some evidence suggests that a second marijuana component called cannabidiol actually has antipsychotic effects. D'Souza said he and other researchers are testing whether administering cannabidiol by itself can alleviate psychotic symptoms.

"If there's enough evidence to support it's use as an antipsychotic," he said, "then that might be one way of getting people to stop using cannabis."