Hi SamGuzman
I have been on Decapeptyl for two years and it is very, very similar to Lupron and is used to suppress hormone production. These GnRH analogues typically cause a spike in testosterone (T) when you first get them and then T production drops massively. This "spike" can last for two to three weeks.
The important thing about these injections is that you must have continuous coverage. There is no point in getting just one of them, you need to get the next one before this one wears off.
I have been on the 3 monthly version (12 weeks) of decapeptyl so I get my booster at the start of week 11 and my GP administers it (actually her senior nurse does and she is a whizz with a needle).
If coverage is continuous and the injection is administered properly then your T levels should drop.