Both can make you forgetful, but there's growing evidence that THC - the ingredient in marijuana that gets you high - can help fight Alzheimer's disease.
Scientists at the Salk Institute in San Diego, California, have found tetrahydrocannabinol (THC) and other compounds in marijuana can kill off a toxic protein associated with Alzheimer's known as amyloid beta.
"Although other studies have offered evidence that cannabinoids might [protect] against the symptoms of Alzheimer's, we believe our study is the first to demonstrate that cannabinoids affect both inflammation and amyloid beta accumulation in nerve cells," says Professor David Schubert, who led the study.
In Alzheimer's, the brain's cells begin to deteriorate. The body produces amyloid beta to stop it, but this eventually builds up and makes the problem worse.
The researchers studied nerve cells engineered in the lab to produce high levels of the toxic protein. Exposing the cells to THC not only lowered the amount of amyloid beta present, but also reduced inflammation.
"Inflammation within the brain is a major component of the damage associated with Alzheimer's disease, but it has always been assumed that this response was coming from immune-like cells in the brain, not the nerve cells themselves," says Antonio Currais, who co-wrote the study.
"When we were able to identify the molecular basis of the inflammatory response to amyloid beta, it became clear that THC-like compounds that the nerve cells make themselves may be involved in protecting the cells from dying."
It's still not certain if smoking marijuana will have the same effect as directly exposing the cells to THC - these cells were grown in the lab, not in living human beings.
There are about 30,000 people in New Zealand with Alzheimer's, a number that's predicted to rise dramatically as the population ages. Southern Cross estimates by 2031, there will be 70,000 Kiwis with Alzheimer's.
The study has been published in journal Aging and Mechanisms of Disease.