Limitations

All research methods and techniques have limitations, regardless of whether they use non-human animals or not.

Firstly, there are ethical concerns. Non-human animal suffer in experiments. At a minimu, they suffer due to confinement but most often from invasive procedures. It is morally wrong to inflict harm on non-human sentient beings.

Ethical issues with human subjects are less pervasive but may occur. For example, in the lack of genuine informed consent and the harmful effects of some drug trials. The use of embryonic stem cells is problematic as the embryo dies when cells are harvested. Some believe that it is morally wrong to put an end to the possibility of human life.
This research is tightly controlled in legislation and stem cells from other body parts can be used. In 2006, Japanese scientist Shinya Yamanaka and colleagues took ordinary adult skin cells and reprogrammed them back into the most basic form of stem cell - a pluripotent stem cell. Now stem cells can be created from adult skin cells, then turned into whatever cell type is needed, such as cardiomyocytes for hearts, glial cells for brains, islet cell for the pancreas and cells that make teeth and bones. Treatments are likely to follow this research. However
there is still a way to go with costs high.

Early studies in vitro and in silico did not give information about complex interactions of living system.
As the technology improves this weakness is being overcome.

The British Medical Journal lists the following methodological problems with animal experiments:
- Disparate animal species and strains, with a variety of metabolic pathways and drug metabolites, leading to variation in efficacy and toxicity
- Different models for inducing illness or injury with varying similarity to the human condition.
- Variations in drug dosing schedules and regiment that are of uncertain relevance to the human condition.
- Variability in the way animals are selected for study, methods of randomisation, choice of comparison therapy (none, placebo, vehicle), and reporting of loss to follow up.
- Small experimental groups with inadequate power, simplistic statistical analysis that does not account for potential confounding, and failure to follow intention to treat principles.
- Nuances in laboratory technique that may influence results may be neither recognised nor reported - eg methods for blinding investigators
- Selection of a variety of outcome measures, which may be disease surrogates or precursors and which are of uncertain relevance to the human clinical condition.
- Length of follow-up before determination of disease outcome varies and may not correspond to disease latency in humans.

Pound, P et al 2004 'Where is the evidence that animal research benefits humans?' British Medical Journal, 328, pp. 514 - 517.