Drug stability can be affected by light, moisture, oxygen, temperature, and other factors. About 25% of drugs on the market today have some requirement for light-resistant packaging. The rate of drug degradation varies from rapid to slow among different categories and examples of drugs. When compounding very light-sensitive drugs, environmental controls should be implemented and exposure to any light may need to be minimized. Packaging of the final compounded product is critical as well as light protection during storage, distribution, and when held at the patient's home for administration. Pharmacists have access to different sources of information that provide information on which drugs need protection from light.