Are slimming sprays dangerous?

I got a mail from a LIB reader asking me to warn people who are trying to lose weight to stay away from slimming sprays. Slimming spray is a slimming drug that is sprayed into the mouth and makes the user lose appetite for days. According to the reader, once you stop using it, it could lead to illness. One of her friends who used it for months recently passed away and she asked me to warn others.

This is the first time I'll be hearing about slimming sprays. Is it really dangerous?