That is one of my arguments against homeopathy: We've got a world full of bright young medical students looking for cheap and easy research to do that will lead to positive results. If they haven't proven homeopathy effective, it's because it isn't.
You can't show something as simple as aspirine 'works' by setting up a lab experiment without test subjects. And as soon as you involve those, it becomes legally complex, expensive, time consuming and hard.
You simply can't compare medical experiments to physics experiments. A physics experiment can be set up to be extremely controlled. If you observe some effect, the number of things it could be due to is very small.
A medical experiment requires people with all their messiness and possibly confounding variables. If you observe some effect, there are zounds of possible explanations. Controlling for all of them requires many test subjects. That makes it expensive, time consuming and hard.
Even a medical experiment on human cells in a petri dish is infinitely more complex than a physics experiment, in terms of variables involved.
Homeopathy doesn't claim that "some substance heals people". It claims (according to Wikipedia [1]) "a substance that causes the symptoms of a disease in healthy people will cure similar symptoms in sick people".
It's fundamentally flawed, and despite revisionist practitioners, has not yet managed to raise it's head above "pseudoscience" status.
It shouldn't really be mentioned in the same sentence as research that is actually trying to determine if a substance has an effect, even if that research is flawed. Said research and homeopathy aren't really playing on the same field. It's like calling religion a science. It's based on a premise that can't be questioned without throwing out the entire idea.