I had a couple of blocks. The first was a little more than 6 months after my injury and it had very little impact on my rsd...the temperature changes were reduced significantly afterwards but pain remained about the same. No negative reactions. 2 years later I had a series of blocks done...and the last block caused me to get worse and my rsd to spread to almost full body. I am mad at myself because I let the dr bully me into it when I didn't really want the treatment...but it's on me for letting myself get pushed around. I think getting worse is pretty rare...and any treatment can make you worse so this is not a huge thing to worry about...but it is a risk even if a small one and it does happen. Blocks seem to generally be MOST effective in the first 6 months and can help people achieve remission. But like everything else you need to look at the positives and the negatives and decide if it's worth the risk. I had bad luck but far more people do have success and relief from the treatment.