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Stem cells have great potential in treating patients with currently untreatable conditions, growing organs for transplants, and in scientific research. But there are clinical, ethical and social issues with their use. These issues will be different for growth and transplant of adult, embryonic and therapeutically cloned stem cells. They will also depend on whether the stem cells are to be used for therapy or research. The benefits of the therapy must be weighed up against any risks and ethical concerns.

It is important to obtain a balanced view. Sometimes, there are no right or wrong answers, or even answers at all.

Some variables which would be considered when discussing stem cells include:

Clinical issues

• There is no guarantee how successful these therapies will be, for example, the use of stem cells in replacing nerve cells lost in Parkinson's disease patients.
• The current difficulty in finding suitable stem cell donors.
• The difficulty in obtaining and storing a patient's embryonic stem cells. These would have to be collected before birth - some clinics offer to store blood from the umbilical cord when a person is born.
• Mutations have been observed in stem cells cultured for a number of generations, and some mutated stem cells have been observed to behave like cancer cells.
• Cultured stem cells could be contaminated with viruses which would be transferred to a patient.

Ethical issues

• A source of embryonic stem cells is unused embryos produced by in vitro fertilisation (IVF).
• For therapeutic cloning, is it right to create embryos for therapy, and destroy them in the process?
• Embryos could come to be viewed as a commodity, and not as an embryo that could develop into a person.
• At what stage of its development should an embryo be regarded as, and treated as a person?

Social issues

• Educating the public about what stem cells can, and can't do, is important.
• Whether the benefits of stem cell use outweigh the objections.
• Much of the research is being carried out by commercial clinics, so reported successes are not subject to peer review.
• Stem cell therapies are expensive and only in their developmental stages. Patients could be given false hope of a cure.

Stem cells can divide to produce new cells, which can then divide into different cell types. Medical treatments with stem cells can treat patients by replacing damaged tissues or cells. So they can help conditions such as diabetes and paralysis. There are some risks using stem cells for medical treatments, such as the transfer of viral infections. Some people also have ethical concerns or religious objections to their use. These are often based on the use and destruction of human embryos in stem cell research. So the medical benefits must be considered alongside these risks and concerns. The use of stem cells is therefore regulated by governments in many countries.

Ideas about science - weighing up arguments

The cloning of human embryos is a difficult and contentious topic with no clear 'correct' answers. When discussing the subject it is useful to address the following:

• State clearly what the issues are. An example would be that some human embryos will be destroyed during the therapeutic cloning process.
• Summarise different views that might be held from both sides of the argument.
• Identify and develop arguments based on the idea that the right decision is the one that has the best outcome for the majority of people.
• Also identify and develop arguments based on the idea that certain actions can never be justified because they are unnatural and wrong. For example, some people think that, no matter what the benefits are of curing a disease, we should not clone embryos because destroying human life is always wrong.

The use of stem cells in research and medicine is carefully regulated by laws made by the government in most countries.