People who smoke marijuana have abnormal changes in the bloodflow in their brains, even after quitting the habit for a month in some cases, says a new government study.1 The findings could help explain why marijuana users face problems with thinking or remembering, as has been reported in other research, say government investigators.
The government study was published last February in the journal Neurology.
"Over the last ten years, we have been systematically studying the psychological, psychiatric, and neurological effects of prolonged use of various abused drugs," explained Ronald Herning, PhD, the study's lead investigator with the National Institute on Drug Abuse at the National Institutes of Health, in an interview with Priority Healthcare.
Cannabis: Therapy or Threat?
Marijuana has been used as a medical treatment for thousands of years. Despite a U.S. federal law banning the use of cannabis, its proponents contend the controversial plant effectively treats pain, nausea and other side effects of medical treatment.2
Some people with MS use marijuana primarily as a therapy for certain symptoms, such as tremors, muscle spasm, and pain. But research on its effectiveness is still controversial. Some scientists maintain more research is needed to prove the usefulness of the drug for this indication.2
Further, studies evaluating the effectiveness of cannabis for this disease have been mixed.3-5
Marijuana's key ingredients that exert the effects experienced are known as cannabinoids. When the drug is smoked or ingested, these components attach to cells in your body, causing the cells to take certain actions. Some of these cells are located in areas of the brain that control body movement, memory, and vomiting. This helps explain why marijuana use affects balance and coordination, and impairs short-term memory and learning, experts say. But experts contend this also explains why the drug may be useful in treating nausea, pain, and loss of appetite.2
Effects on Brain Bloodflow
To evaluate the effects that marijuana use has on brain-related bloodflow, scientists recruited more than 70 patients to take part in a month-long inpatient program. Most were marijuana users. They were compared to 18 patients classified as non-users. The marijuana users were told to be abstinent during the study.
Each patient's brain bloodflow velocity was measured at the start of the research, and again at the end of the study in those who had been using marijuana.
When the data were analyzed, Herning and his team found that bloodflow velocity was significantly higher in those who had been using the drug compared to the second group. Those in the marijuana group also had higher levels of blood resistance in their brain arteries. This is due to the narrowing of blood vessels that occurs when the circulatory system is unable to regulate itself properly, the researchers explained.
"The marijuana users had [blood resistance] values that were somewhat higher than those of people with chronic high blood pressure and diabetes," said Herning. "However, their values were lower than those with dementia." In any case, the result was less bloodflow to the brain.
Abstinence Did Not Improve Effects in Some
Blood resistance tended to improve after a month of abstinence for those who were in the marijuana group, the investigators found, but only among those who were considered light to moderate marijuana users. There was no improvement among those classified as heavy users.
Light users smoked two to 15 marijuana cigarettes per week. Moderate users were classified as those smoking 17 to 70 marijuana cigarettes weekly. Heavy users smoked 78 to 350 marijuana cigarettes per week.
"We do not know the mechanism by which marijuana produces these effects," Herning told Priority Healthcare. However, he added that the potential long-term consequences of this increased bloodflow resistance include an increased risk of "neuron loss, cognitive impairments, and stroke in these young individuals."
It is possible that the bloodflow changes that remained after a month of abstinence in the heavy marijuana users might improve beyond that time, but that hasn't been researched as yet, Herning said. "This question may only be answered by testing former marijuana abusers."
1. Herning RI, Better WE, Tate K, Cadet JL. Cerebrovascular perfusion in marijuana users during a month of monitored abstinence. Neurology 2005 Feb 8;64(3):488-93.
2. Mayo Foundation for Medical Education and Research. Marijuana as Medicine? Pros and Cons. Available at: http://www.mayoclinic.com/invoke.cfm?id=GA00014. Accessed June 16, 2005.
3. Robson P. Therapeutic aspects of cannabis and cannabinoids. Br J Psychiatry 2001 Feb;178:107-15.
4. Page SA, Verhoef MJ, Stebbins RA, Metz LM, Levy JC. Cannabis use as described by people with multiple sclerosis. Can J Neurol Sci 2003 Aug;30(3):201-5.
5. Fox P, Bain PG, Glickman S, Carroll C, Zajicek J. The effect of cannabis on tremor in patients with multiple sclerosis. Neurology 2004 Apr 13;62(7):1105-9.
John Martin is a long-time health journalist and an editor for Priority Healthcare. His credits include overseeing health news coverage for the website of Fox Television's The Health Network, and articles for the New York Post and other consumer and trade publications.
