Medicines and medical procedures have to be tested on living creatures in order to determine whether or not they are safe. If they are not tested on animals, then they must be tested on humans. I think a human being's life is far more important than any animal's life, so it's better to test on animals than on humans.
Yes, it is justifiable to perform medical experiments on animals in order to provide medical benefits to humanity. Our long-term survival has more of a moral imperative than that of animals. With that said, it is important to follow best practices of humane handling when running the experimental processes on the animals.
Yes, humans should respect animals and animal life. However, even the Bible says that humans should have dominion over the animals of the Earth. The life of an animal isn't worth that of a human. If there's a rabbit in the middle of the highway and I'm traveling at 70 MPH, I'm not swerving my car to avoid it because there is a risk I could hurt human beings while doing so. It's that kind of concept that makes this a very simple question to answer.
Yes, experimentation on animals due to medical incentive is morally justifiable, because it is better for a human to find relief, even if an animal has to suffer. Experimentation on animals is a good way to filter out problems before the medicine or the remedy is tried on a human. Problems for humans can be avoided.
Given that the alternative is to test directly on humans, I believe it is justifiable to experiment on animals for medical incentive, especially when considering pharmaceuticals. I understand people don't like this because they don't want the animals to be harmed, but the alternative is far more drastic and unreasonable given this option.
"In vitro (in glass) testing, such as studying cell cultures in a petri dish, can produce more relevant results than animal testing because human cells can be used.  Microdosing, the administering of doses too small to cause adverse reactions, can be used in human volunteers, whose blood is then analyzed. Artificial human skin, such as the commercially available products EpiDerm and ThinCert, is made from sheets of human skin cells grown in test tubes or plastic wells and can produce more useful results than testing chemicals on animal skin.  Microfluidic chips ("organs on a chip"), which are lined with human cells and recreate the functions of human organs, are in advanced stages of development. Computer models, such as virtual reconstructions of human molecular structures, can predict the toxicity of substances without invasive experiments on animals."
This is Speciesism. It's like racism or sexism, but with species. Not only can testing be inaccurate because mice have different anatomy (Even a slight bit could throw the experiment off), but the main reason for not experimenting on animals instead of humans is that they are not as valuable, or they are not as smart, then why don't we see mentally ill people with extra limbs? Why don't we see disabled people with laser vision? The rest of us are superior, so why aren't we doing experiments on them? "The case for animal rights" by Tom Regan summarizes my argument: "[It] involves more than merely being alive and more than merely being conscious. ... Individuals are subjects-of-a-life if they have beliefs and desires; perception, memory, and a sense of the future, including their own future; an emotional life together with feelings of pleasure and pain; preference- and welfare-interests; the ability to initiate action in pursuit of their desires and goals; a psychophysical identity over time; and an individual welfare in the sense that their experiential life fares well or ill for them, logically independently of their utility for others and logically independently of their being the object of anyone else's interests. Those who satisfy the subject-of-a-life criterion themselves have a distinctive kind of value – inherent value – and are not to be viewed or treated as mere receptacles."