Clinical research that is related to developing products for patient care is divided into two preclinical and four clinical phases, each addressing different questions. The knowledge gained at each phase is assessed before progressing to the next. The table below provides an overview of the process. Click each phase to learn more.

Pharmaceutical research starts in a screening laboratory. Compounds synthesized in the chemical laboratory or extracted from natural substances are screened for therapeutic activity. Depending on the nature of the compound, screening of the compounds might be conducted in vitro (in glass) in non-animal systems such as cell cultures; or in vivo (in life) using animals. Researchers usually have to screen thousands of compounds to find one that works in the screening test. In fact, only one out of 5,000 synthesized products might actually end up on the market. When they find a compound that appears to work, they will pass it on to other researchers to learn more about it.

A lot has to be learned about a compound before humans are exposed to the risk of taking a new drug. If the drug appears to have acceptable levels of safety and effectiveness in appropriate animal models, and a potential market exists for the drug, the drug can enter the clinical phases of development.

Preclinical studies ask the questions:

• How safe is the drug in the animal model?
• Does it appear to have unwanted effects on other biological systems?
• What is the effective dose range (in more than one species or system, if possible)?
• What organs or organ systems does the drug affect? For example, is the drug metabolized (broken down) in the liver?
• How and when is the drug absorbed, distributed, metabolized, and excreted?
• Is the drug a carcinogen (cancer causing)?
• Is the drug a teratogen (an agent that causes birth defects)?