A clinical trial is an experimental study that tests a new treatment on humans to measure its safety and effectiveness. It compares an experimental drug with a placebo or an already approved drug. The goal is to find out if the new drug is better and more effective than current treatments.

Clinical trials help advance medicine and science by studying diseases in a controlled way, which leads to better treatments. For example, in cancer trials, progress might seem slow, but every small improvement adds up to more effective treatments and a better quality of life for patients.

Before a new drug can be approved for humans, it must be tested in labs and on animals to assess safety. This is called the preclinical phase. If successful, it moves to clinical trials, starting with healthy people and then moving to patients with the targeted condition. The drug will go through several phases, and only those that meet the set goals for safety and effectiveness will be approved for use. Only one in 10,000 compounds becomes a drug, and the process can take 10-12 years, with high costs.

Participants must meet specific medical criteria, known as inclusion and exclusion criteria, defined in a study protocol. Being selected does not mean there are no other treatment options, but the doctor may believe it's a good opportunity. Participation is voluntary, and patients can withdraw at any time.