Pure THC is prescribed under the brand name Marinol and truly helps people every year. However, it has structural differences from the THC found in Cannabis and also lacks the modulating compounds (see paper on Synthetic THC by Dr Alex Shulgin). Only mother nature can create many of the compounds found in cannabis but real research is essentially prohibited.
In 1936, the year before the ban, there were over 40 registered medications produced by companies like Bayer and Merck directly derived from Cannabis. The cannabis boom happened the year before prohibition due to the invention of a processing machine (hemp's equivalent to the cotton gin). It was predicted to decimate the opium and cotton industries (follow the money). Before that, the US government made films touting the huge benefits of hemp over nearly all old crops. The importance of hemp has been wiped from all history books written after 1960 or so.
Our body has natural cannabinoids that participate in nearly every body function. Similar to opiods but far more extensive and diverse. Prohibiting research of a plant that produces such compounds so close to our own chemistry was a crime committed by a self-serving, corporate-owned government against all people.
The only people who claim that Marinol helps people are the people who sell it.
I went through a hellish 5 months of chemo/radiation treatment a year and a half ago, and I finally gave in to trying smoking a little weed. It relieved my nausea within seconds. I mean nearly instantly. So I asked the doc for a Marinol rx, and all it did was make me high for 12 hours, with no nausea relief whatsoever. It is synthetic, suspended in oil and contained in a gel-like ball. It is useless as a nausea drug. (I should add that none of the other drugs they gave me had any effect on the nausea either.)
There is something in the smoke that is not in the Marinol. And that something is the key. I still have lasting intestinal effects from the treatments, and I still keep some weed around for when it gets bad. I wouldn't be without it, even though I only use it once in a while.
It is too bad the stoners have ruined it for the people who could really benefit from it. Yes it has side effects (it makes you high), but so do narcotics, and they give them out like candy if you have pain.
If anyone reading this ever finds themselves undergoing cancer treatment, get your hands on some weed and a pipe (or better yet, a vaporizer.) It saved my life because it allowed me to drink fluids and eat a little. It is just sad I had to buy it from the creepy guy down on the corner, and worry about getting arrested.