 When you get sick, do you ever wonder where medicines come from? Behind every pill, injection, or cell-based therapy you might be given lie decades of laboratory research and hundreds or thousands of failed experiments along the way. Once potential treatments are discovered, they are subjected to rigorous testing in animals and the most promising treatments are then tested in humans to make sure that they are safe and effective. Ultimately this process takes the innovation and ingenuity of hundreds of scientists together with billions of dollars of research and testing. The treatment's journey from the bench where it is discovered to the bedside when it can actually treat patients has several stages that culminate in a thorough clinical trial. Clinical trials are research studies in humans that explore whether a medical treatment is safe and effective for people. In the U.S., these studies and the important data they generate are approved, regulated, and evaluated by the Food and Drug Administration, the FDA. The best clinical trials are performed as randomized double-blind controlled trials. This means that patients are split into two groups. One group receives the experimental treatment and the other group receives a placebo, an intervention that has no therapeutic effect, or a current standard of care. The purpose of this design is to make sure that the experimental treatment itself is responsible for differences, not just the perceived improvement of a placebo. Double-blind means that neither the patient nor the doctor knows what group the participant is in. Before undergoing any treatment, all participants of clinical trials go through a process called informed consent, designed to make sure they understand the potential benefits and risks of experimental treatment as well as those of the placebo or standard of care. In accordance with the FDA's requirements, human clinical trials have four phases that each has a specific purpose. Phase one trials, which can last up to two years, test whether a new treatment is safe and well tolerated, including side effects. Phase two trials, which can last longer than two years, test the treatment to see if it is effective. Is it doing what we hope it will do? And to further evaluate its safety in more patients. Phase three trials are the most critical evaluations and are performed on a larger group of people to understand whether the treatment works to prevent or treat disease better than any alternative treatment. This is called the treatment's efficacy. They typically last three to five years. After a phase three trial, if the treatment has demonstrated sufficient evidence of positive benefit, it can be approved by the regulatory agency, the FDA in the United States, and can be commercialized. Phase four trials are done that monitor safety for any rare or long-term side effects of the treatment. Phase four also evaluates the treatment's effectiveness in real-world situations. Regardless of the outcome, participation in clinical trials is always valuable and brings us closer to curing or mitigating disease. In most cases, it takes more than a decade for a candidate therapy to move from phase one testing to real-world distribution. In that context, the progress of California scientists and physician scientists is especially remarkable. Since the passage of Proposition 71, the California Stem Cell Research and Cures Act of 2004, 30 human clinical trials have been completed, are in progress, or are getting ready to start within the next few months. We must remember that human trials will celebrate successes. The barriers will surface along with complications and challenges, so patients and understanding of the scientific discovery process are essential. This is especially true as California scientists work to develop a new generation of therapies, cellular therapies, that will have unique challenges that differ from traditional drug-based medicines. Clinical trials are absolutely necessary to determine that a treatment is safe and that it has a real positive effect on a particular disease, better than not observed by a placebo or the standard of care. Going forward, we must build on the progress that California's remarkable scientists and physician scientists have made. Only with continued support for biomedical research can we bring the most innovative therapies to the patients who need them most. To learn more about clinical trials, check out the ISSCRs, a closer look at stem cells.