Scientists working to perform research cloning require large numbers of women's eggs for their efforts. Egg retrieval is invasive, time-consuming, uncomfortable, and—most important—puts women at risk of significant adverse reactions.

In order to procure eggs, researchers give women hormonal drugs to first "shut down" and then "hyperstimulate" their ovaries to produce more eggs than normal. These eggs are then surgically extracted.

Egg retrieval for assisted reproduction has been conducted for several decades, but there is inadequate data on its risks. Follow-up studies on long-term risks are particularly lacking; those that do exist are inconclusive.

Short-term reactions to one commonly used "shut-down" drug include severe joint pain, difficulty breathing, chest pain, depression, amnesia, hypertension, and asthma. The drugs used to stimulate multiple egg production can cause ovarian hyperstimulation syndrome (OHSS), which is often a mild reaction but which can become serious enough to require hospitalization and, rarely, to cause death.

Some women's health advocates and others have questioned whether researchers should ask women to expose themselves to these risks, especially in light of the early and speculative stage of cloning research. Proposals to pay women to provide eggs for research remain controversial, as this practice could tempt economically vulnerable women to take risks they otherwise would avoid.