Human reproductive cloning – producing a genetic copy of an existing person using somatic cell nuclear transfer – has never been done. Many scientists believe that it can never be safe. In opinion polls, , overwhelming majorities consistently reject its use. The U.S. has no federal law on human reproductive cloning, but several states, dozens of countries, and international agreements prohibit it.
Research cloning – producing cloned human embryos from which to derive embryonic stem cells (theoretically for customized medical treatment or research) – has been supplanted by techniques to derive pluripotent stem cells from somatic cells. Concerns raised by research cloning include its reliance on large numbers of women’s eggs (involving risks that are understudied and often downplayed), unrealistic claims about “personalized” therapies, and the need for effective oversight to prevent rogue use of cloned embryos for reproductive human cloning.