We have known for a long time that the reason morphine helps block pain perception is that in the body there are naturally-produced morphine-like chemicals called endorphins that do the same by blocking pain signal transmission. Marijuana has a similar though less potent effect on pain. Some of my patients with non-malignant pain have confided in me that they find marijuana effective in reducing their pain. The scientific literature suppports this view. Unfortunately marijuana and marjuana-like medicines (collectively known as cannabinoids) also have psychoactive effects and in most people stimulate appetite. This appetite enhancement (and anti-emetic effect) is useful in HIV AIDS patients but not in most people with non-malignant pain.
The psychoactive effect is due to an increased dopamnine effect of marijuana--increasing awareness of ordinary events such as music at a rock concert. Unfortunately, while this may make the experience of listening to music more pleasurable, long term studies of the effect of natural marijuana in teen-agers has shown a tendency to develop schizophrenia, a psychosis characterised by paranoia and visual and auditory hallucinations. Some smokers may experience such symptoms temporarily and these may well be the ones at risk for later schizophrenia. Teen-agers are particularily prone to later schizophrenia but older adults have not shown this tendency--so far.
It is the THC (Tetra Hydro Cannabinol) component of marijuana that stimulates the release of dopamine, and there is an antagonist in marijuana called CBD (Cannabadiole). Whereas in the 1960's THC concentration was only 1 to 3%, in the current crop the THC is 16 to 25%. So today's marijuana is much more likely to be schizophrenogenic than in the Woodstock era. This is the result of selective breeding.
Genetics also plays a role in the development of schizophrenia. The COMT gene regulates the dopamine level and there are two alleles (= variants)of this gene that may occupy the same place on that chromosome. These are called Met (Methionine) and Val (Valene). If one chromosome has Met and the other chromosome has Val at the appropriate site on the other chromosome the chance of getting schizophrenia from smoking marijuana doubles what it would be with two Vals. Two Vals increase the chance of schizophrenia five times over two Mets.
The natural-occuring cannabinoids are called "endocannabinoids" and examples are anadamide and and 2-arachidonyl glycerol. They have are believed to reduce allodynia (pain due to normally non-painful stimuli) and hyperalgesia (increased pain due to normaly painful stimuli) that are characteristic of chronic pain when central sensitization has occurred. See Hohmann and Suplita, Endocannabinoid mechanism of pain modulation, AAPSJ 2006, 8: E693-708 for details. These scientists have shown that environmental stress mobilizes these chemicals and to me this helps explain why a broken ankle seems to cause little pain in a burning building where saving one's life is of primary importance.
In the first picture on this page we see endocannabinoids (the little red things) being released from the post-synaptic nerve cell (lower on the diagram) in a series of pain fibres in order to counteract the pain signal (in yellow) comimg from a peripheral source. In the next picture, as it attaches to the neuron that is bringing the sense of pain toward the brain, the pain signal is reduced--not actually blocked, but reduced in intensity--as they bind to the CB1 receptors.
Cannabinoid receptors so far detected are of two kinds named CB1 and CB2. CB1 receptors are found in the central nervous system and in other tissues such as fat cells (where they affect appetite) and parts of the gastrointestinal tract. Much less is known about the action of marijuana on CB2 receptors but these receptors are found on immune cells and affect immune modulation through cytokine release. This is important in the treatment of multiple sclerosis, which is an inflammatory disease of the central nervous system. Our concern here is with regard to CB1 receptors.
Thanks for these beautiful pictures is due to Bayer Pharmaceuticals who manufactures Sativex, a marijuana-like chemical that contains both THC and CBD. Because Sativex is sprayed under the tongue it lacks the harmful effect on the lungs of smoking marjuana. When marijuana is eaten, about 50% is destroyed by the liver before CNS effects are achieved and satifex also avoids this disadvantage because it gets into the blood stream directly through the mucosa of the mouth instead of through the digestive system whose venous blood all passes through the liver.
I have been told by a knowledgable medicinal cannabis user that when eaten (clean organic and flushed of chlorophyl), cannabis is converted from delta 9 THC into Delta 11 THC which is both more psychoactive and potentially has a longer duration of action.
The last picture on this page shows the components of Sativex binding to the endocannabinoid receptors on the primary pain fibre. There they compete with endocannabinoids and bring about further down-regulation of pain signal transmission, that is, they dimish the pain.
Now you have several options: