Roughly 20% of the people who come for a cannabis consultation now are dementia patients, says Dr. Jeffrey Hergenrather, a general practitioner in Sebastopol, Calif., who has made cannabis his specialty for more than 25 years. Some dementia patients—and their caregivers—are seeking alternatives after traditional medications haven’t provided relief or caused unsettling side effects, doctors say.

Questions and risks

Cannabis can lead to drowsiness, which raises the serious risk of falls in older people with dementia. That drowsiness can further weaken cognitive functioning in Alzheimer’s patients, says Dr. Jacobo Mintzer, a psychiatrist and professor at the Medical University of South Carolina who is researching cannabis treatment in dementia patients. 

Most doctors who support cannabis for dementia currently recommend it for people in the middle to late stages of the disease. They say further study is needed to see if it can be used in earlier stages, and to weigh benefits with potential risks. 

They typically prescribe THC, the main psychoactive component of marijuana, in combination with CBD, another part of the cannabis plant that doesn’t produce a high. CBD can decrease the psychoactive effects of THC and enhance the positive properties, Mintzer says.

A new National Institute on Aging study is evaluating a combination of CBD and THC in late-stage hospice-eligible dementia patients who suffer from severe agitation. Typically, they are treated with antipsychotics. But those have side effects including severe constipation, confusion and sometimes even increased agitation, says Mintzer, who is principal investigator of the study.

What the science says

There isn’t much definitive research on cannabis and its impact on cognitive impairment and dementia, says Dr. Ronald Petersen, a professor of neurology at Mayo Clinic College of Medicine and Science in Rochester, Minn. Still, he has had patients and caregivers ask about it and hasn’t discouraged them from taking it. 

“Sometimes it can produce a calming effect for people,” he says, noting that it isn’t clear whether it does anything to treat the underlying disease. 

A recent study of 75 Alzheimer’s patients indicated, in preliminary results, that 5 milligrams of synthetic THC twice a day significantly decreased agitation, compared with the placebo. The researchers, from Johns Hopkins University School of Medicine and Tufts University School of Medicine, presented the findings at several conferences this year and are preparing them for publication. A 2019 study had similar findings, but also reported increased drowsiness among some people.