The Reference Manual on Scientific Evidence, Third Edition has the following to say about animal studies:
Animal studies have a number of advantages. They can be conducted as true experiments, and researchers control all aspects of the animals' lives. Thus, they can avoid the problem of confounding, which epidemiology often confronts. Exposure can be carefully controlled and measured. Refusals to participate in a study are not an issue, and loss to followup very often is minimal. Ethical limitations are diminished, and animals can be sacrificed and their tissues examined, which may improve the accuracy of disease assessment. Animal studies often proved useful information about pathological mechanisms and play a complementary role to epidemiology by assisting researchers in framing hypotheses and in developing study designs for epidemiologic studies.
Animal studies have two significant disadvantages, however. First, animal study results must be extrapolated to another species - human beings - and differences in absorption, metabolism, and other factors may result in interspecies variation in responses. For example, one powerful human teratogen, thalidomide, does not cause birth defects in most rodent species. Similarly, some known teratogens in animals are not believed to be human teratogens. In general, it is often difficult to confirm that an agent known to be toxic in animals is safe for human beings. The second difficulty with inferring human causation from animal studies is that the high doses customarily used in animal studies require consideration of the dose-response relationship and whether a threshold no-effect dose exists. Those matters are almost always fraught with considerable, and currently unavoidable, uncertainty.
It turns out that there's a third significant disadvantage and one that ranks ahead of the other two. It's nicely summed up in the title of a new article in Nature - "Animal studies produce many false positives." Put another way, before you start arguing about whether the result of a particular animal study is relevant to the effect of some chemical in humans you need to assess whether the study is even reliable in the first place. That's because the number of animal studies showing statistically significant results is far higher than would be expected by chance alone. In fact, it's almost double what you'd expect to find if hypotheses were being fairly tested in animals and the results invariably reported.
Interestingly, small sample size and financial interest seem to correlate with what appears to be p-hacking and/or selective publishing. Thus as we've said previously, you should assume the p-hacking scandal won't be limited to academia. The article is "Evaluation of Excess Significance Bias in Animal Studies of Neurological Diseases" and it sensibly ends:
In conclusion, the literature of animal studies on neurological disorders is probably subject to considerable bias. This does not mean that none of the observed associations in the literature are true.