In my opinion it's kind of a spirit rather a cure medicine.
It's a complete system of life and part of it can be performing HIjama.
May be it can be done for several reasons, but to have a complete wellness, possibly our mind, heart and belief will play a much bigger role.

Example: The second command of Islam is prayer, but if I am trying to figure out a matter like covering face is good or bad without following the second command is a question mark.

It's similar in any other matter. If the vehicle is heating the complete cooling system should be in order. Other wise just cleaning the radiator may help some time & it may not.

So, my point is- Hijama can be more effective when it's done through on a spiritual format or some one following a life which leads to do a Hijama.

How ever I have no objection just some one drop in and do a Hijama. But the effect is only the person who does the Hijama knows.

The above is my personal opinion only.