There are a variety of reasons why scientists experiment with animals ranging from cosmetic to behavioural and pharmaceutical. Some of these are easier to justify than others but there are also alternatives to animal testing that need to develop further.
One reason for testing on animals is for the development of new cosmetics. This has generated a great deal more criticism than others as it is much more superfical. Critics argue that these new products are largely unecessary and that the suffering of animals does not justify the end product. Furthermore there are many cosmetics that have developed without the need for animal tests.
Another of the most common reasons for animal testing is new drugs. These drugs are used to treat both animals and humans. Indeed, we can now cure many illnesses because of animal testing and it is for this reason that proponents of animal testing argue that they are so vital. Although, this argument values the lives of humans above the suffer of animals.
However, alternatives to animal testing do exist. Over the last few years there were scientific breakthroughs with regards to improvements in testing on cells. If these were to be extended there will be no need for any animals to suffer. Another possibility is to use computer models to test new items.
In conclusion, for some people the testing of pharmaceutical drugs on animals is justified and appropriate. Although I would agree with this to an extent and would argue that human lives are more important than animals, I also think that the alternatives to animal testing need to have further development.