Injecting marijuana is something I wouldn't do. For one, how fun is it to feel a prick in your arm and carefully slide a needle into one of your main veins? Doesn't sound like much fun to me. Anything that would be injected would have to be synthezized THC, not actual THC cabbanoids from a plant...I think anyways.

And yes, there is a new medical spray out there called "Sativex" Here is their site:

www.sativex.com

Although, from reading about synthetic THC, it is found not to be as effective as actually smoking the real deal.