Age-related diseases of the brain are typically characterized by changes in inflammatory responses during disease progression. Inflammation in the brain is mediated by microglial cells, and treatments that target these cells can protect neurons from damage that leads to degeneration. Multiple Sclerosis, Parkinson's, and Alzheimer's disease are neuro-degenerative conditions for which cannabis and cannabinoid therapies show promise, both for treating the symptoms and the underlying disease by targeting microglial cells through cannabinoid receptors.
Oxidative stress in the brain is a major hallmark of motor and neurological diseases such as Parkinson's and Alzheimer's disease. Cannabinoids are able to protect neurons from oxidative damage. Alzheimer's disease, characterized in part by a decrease in the production of new neurons, and is also associated with oxidative stress due to the membrane action of beta-amyloid peptide aggregates. A laboratory study published in 2004 indicates that one of the cannabis plant's primary components, cannabidiol (CBD), exerts a combination of neuroprotective, anti-oxidative and anti-apoptotic effects by inhibiting the release of the toxic beta-amyloid peptide.
Furthermore, recent studies suggest that endocannabinoids may control the growth and maturation of new neurons through the CB1 receptor. Therefore, cannabinoids could reduce inflammation and protect brains in age related neurodegenerative conditions such as Alzheimer's disease. The neuroprotective action of cannabinoids appears to result from their ability to inhibit reactive oxygen species, glutamate, and tumour necrosis factor. THC, CBD, and synthetic AM404 all contain phenolic groups in their chemical structure and are thus able to reduce radical oxygen species. Notably CBD has extraordinary antioxidant properties and can effect Calcium homeostasis, both of which lead to positive effects against a wide range of neurodegenerative diseases.
Another cannabinoid, THC, has also has been shown to reduce the agitation common to Alzheimer's sufferers, according to findings presented in 2003 at the American Society of Consultant Pharmacists' 34th annual meeting. Agitation is the most common behavioural management problem in patients with Alzheimer's and affects an estimated 75 percent of people with the disease. It may lead to a variety of symptoms ranging from physical and/or verbal abusive postures, physically non-aggressive conduct including pacing and restlessness, as well as verbally disturbed behaviours such as screaming and repetitive requests for attention.
This study and the Institutes of Medicine report also show THC to be effective in combating the anorexia or wasting syndrome common to Alzheimer’s sufferers, since food refusal is a common problem inpatients who suffer from Alzheimer's type dementia. The appetite-stimulation properties of cannabis are some of the most well-established in clinical research.
Few clinical trials have looked at Cannabinoids and Parkinson's disease. However, research has shown that 25% of Parkinson's patients smoke cannabis and 46% of these patients report improvement resulting from side effects of long term levodopa treatment.  A randomized placebo controlled study using extracts of cannabis produced significant improvements in patients' cognition. The authors note that they did not see improvements in pain or sleep disorders. They speculate that the oral route (versus inhaled route) of cannabis ingestion leads to too much variability of cannabinoids in blood.
Cannabinods represent an emerging therapeutic option that could be available in the near future. Plant cannabinoids such as CBD have been effective in experimental models of Alzheimer's, Parkinson's, and Huntington's disease.[189, 190] Cannabinoid therapies are still in an early phase of development, but research suggests that they can be useful drugs for the treatment of many diseases.
This new research on cannabis and neurodegenerative diseases, coupled with the extensive work done on other neuroprotective and neurogenic qualities of cannabis and its components, indicates that cannabis may become the source of the most effective treatments for battling the Central Nervous System diseases that afflict millions of elderly Americans.