Grant C.

1st Medical Studies on Pot in 20 Years Find it Does Relieve Pain

The University of California in San Diego confirms that pot helps with reducing muscle spasms related to multiple sclerosis and pains caused by neurological injuries. In four trials, people suffering from multiple sclerosis, AIDS, or diabetes, and others with pain caused by chilli pepper injections, were given cigarettes with marijuana in them. A large percentage of the people reported that they felt more relieved.
The independent variable was what they were given (regular cigarettes or marijuana); the dependent variable was how what they smoked affected them. I would suggest as a follow-up is a test on other drugs on how they affect the nervous system.