Short-term toxicology studies are carried out to test whether a drug is safe enough to be used for phase I clinical trials. The drug is given to animals at sufficiently high doses to ensure a toxic effect, and the results of these tests are used to determine suitable dose levels for clinical trials. Acute toxicity studies determine the short-term effects of a drug when it is administered as a single dose, or as several doses over a period of 24 hours or less. Subacute toxicity studies are carried out to observe any toxic effects that arise from administering several doses of the drug at levels expected to cause toxicity, but not death. Long-term toxicology tests are carried out to test the drug for chronic toxicology, carcinogenicity, special toxicology, mutagenicity, and reproduction abnormalities. Reproduction studies have to be carried out if the drug is likely to be taken by women of child bearing potential.