Can smoking marijuana prevent Alzheimer's disease?
July 14, 2010
by Gary Wenk, Ph. D
Can smoking marijuana prevent the memory loss associated with normal
aging or Alzheimer's disease? This is a question that I have been
investigating for the past few years. The concept of medical
marijuana is not a new one. A Chinese pharmacy book, written about
2737 BCE, was probably the first to mention its use as a medicine for
the treatment of gout, rheumatism, malaria, constipation, and
So what does marijuana do in the brain? It produces some excitatory
behavioral changes, including euphoria, but it is not generally
regarded as a stimulant. It can also produce some sedative effects
but not to the extent of a barbiturate or alcohol. It produces mild
analgesic effects (pain relief) as well, but this action is not
related pharmacologically to the pain-relieving effects of opiates or aspirin.
Finally, marijuana produces hallucinations at high doses, but its
structure does not resemble LSD or any other hallucinogen. Thus,
marijuana's effects on our body and brain are complex. Just how does
it achieve these effects and are they beneficial? The chemicals
contained within the marijuana plant cross the blood-brain barrier
and bind to a receptor for the brain's very own endogenous marijuana
neurotransmitter system. If this were not true, then the marijuana
plant would be popular only for its use in making rope, paper, and cloth.
The first endogenous marijuana compound found in the brain was called
anandamide, from the Sanskrit word ananda meaning "bliss." Anandamide
interacts with specific receptor proteins to affect brain function.
The great abundance of these receptors gives an indication of
importance of the endogenous system in the regulation of the brain's
normal functioning. Recent investigations have also shown that
stimulating the brain's marijuana receptors may offer protection from
the consequences of stroke, chronic pain, and neuroinflammation.
Surprisingly, it may also protect against some aspects of
age-associated memory loss. Ordinarily, we do not view marijuana as
being good for our brain and certainly not for making memories. How
could a drug that clearly impairs memory while people are under its
sway protect their brains from the consequences of aging? The answer
likely has everything to do with the way that young and old brains
function and a series of age-related changes in brain chemistry. When
we are young, stimulating the brain's marijuana receptors interfere
with making memories. However, later in life, the brain gradually
displays increasing evidence of inflammation and a dramatic decline
in the production of new neurons, called neurogenesis, that are
important for making new memories.
Research in my laboratory has demonstrated that stimulating the
brain's marijuana receptors may offer protection by reducing brain
inflammation and by restoring neurogenesis. Thus, later in life,
marijuana might actually help your brain, rather than harm it. It
takes very little marijuana to produce benefits in the older brain;
my colleague in France, Dr. Yannick Marchalant, coined the motto "a
puff is enough" because it appears as though only a single puff each
day is necessary to produce significant benefit. The challenge for
pharmacologists in the future will be to isolate the beneficial
effects of the marijuana plant from its psychoactive effects.