What is precision medicine?

By considering all aspects of an individual, including their molecular, environmental, economic, and social characteristics, precision medicine aims to provide the most effective and appropriate tests, treatments, and prevention strategies.

Precision medicine is an approach that uses advanced computing tools to measure, combine, and study large amounts of data from various sources–including research, clinics, and communities–to better understand health and disease.

The right treatment, for the right person, at the right time.

Precision medicine–sometimes called "personalized medicine"–places humans at the center of health care. With modern technology and big data, precision medicine integrates all information about an individual to create a clearer picture of their health status. This information can include everything from the mechanisms that drive disease to the social and built environments that affect our physical and mental well-being.

By considering the unique physiological, environmental, economic, and social characteristics of people, precision medicine can provide more effective diagnostics, therapeutics, and preventive care. The precision medicine approach uses advanced computing tools to gather, combine, and study large amounts of data from research, clinical, personal, environmental, and population health settings to better understand health and disease, and to develop and deliver more targeted testing, treatment, and prevention options.

Common Definitions

Precision medicine, sometimes called personalized medicine, is an approach for protecting health and treating disease that takes into account a person’s genes, behaviors, and environment. Interventions are tailored to individuals or groups, rather than using a one-size-fits-all approach in which everyone receives the same care.
Centers for Disease Control
Precision (or personalized) medicine is defined as the application of emergent technologies to better manage patients' health and to target therapies to achieve the best outcomes in the management of a patient's disease or predisposition to disease. Used properly, precision medicine should both improve patient outcomes and deliver benefits to the health service - including reducing the cost of ineffective treatment and multiple tests.

Some definitions expand the concept into precision health:

The vision would be to go beyond Precision Medicine: instead of a frantic race to cure disease after the fact, we can increasingly focus on preventing disease before it strikes. By focusing on health and wellness, we can also have a meaningful impact in reducing healthcare costs...we call this idea Precision Health, where we focus on helping individuals thrive based on all the factors that are unique to their lives, from their genetics to their environment.
Lloyd Minor, PhD, Stanford University
Precision health takes into account differences in people’s genes, environments and lifestyles and formulates treatment and prevention strategies based on patients’ unique backgrounds and conditions.
University of California, Los Angeles

One size does not fit all.

Humans have more in common with each other than we might realize: We are about 99.9% genetically similar. But that remaining 0.1% holds a lot of variation.

Your DNA determines physical attributes, like your eye color, but it can also influence how your body reacts to disease or medications. Other biological mechanisms can also play a part, like your immune system or gut bacteria, which vary between people and can change over time.

External conditions matter, too: exercise, nutrition, geography, history of trauma, pollution, and other factors can affect your health and how your body responds to disease.


Cancer experts used to base treatments solely on the region and stage of the cancer.

Large studies of genes and disease outcomes have shown how individual genetic variations affect cancer patients (e.g., HER2, or PTEN mutations). This research has provided a better understanding of inherited cancer risk and the importance of developing targeted treatment cancer options based on a person's genetic profile.

Mental Health

Health care providers typically diagnose mental health disorders by matching a patient to a cluster of symptoms that often overlap with other disorders. This lack of precision in diagnosis, combined with the fact that treatment responses vary widely across individuals, means practitioners must often use a trial-and-error approach. An urgent need to improve mental health diagnoses, prevention, and treatment models demands that we combine psychiatric approaches with neurological tests (e.g., brain scan images, blood samples) and incorporate the social determinants of health.


Individual responses vary among those with COVID-19, ranging anywhere from asymptomatic to severe and long lasting. Many unresolved questions remain about COVID-19's impact on our health. For example:

  • Why do pre-existing conditions influence disease progression?
  • What causes long-term COVID symptoms in some patients but not others?
  • How do environment, diet, or other external factors affect COVID-19 outcomes?

Approaches rooted in precision medicine will help answer these questions.

How does precision medicine affect me?

"Historically, most medical treatments have been designed for the average patient—too often not reflecting the likely diversity and patient mix in the real-world setting. This is changing with the emergence of precision medicine, an innovative approach to disease prevention, early detection, and treatment that takes into account individual differences in people’s genes, environments, and lifestyles."

–Dr. Irene Dankwa-Mullan, "Precision Medicine and Health Disparities: Advancing the Science of Individualizing Patient Care"

Case Study: Multiple Sclerosis

Today's Situation

When Jennifer received a multiple sclerosis (MS) diagnosis, she faced a hard choice: Should she start a disease-modifying drug right away to delay nerve damage, or wait until her symptoms got worse, since the drug would eventually lose its effectiveness? Jennifer's doctor suggested she start with the most common standard treatment. A month later, Jennifer switched drugs because of substantial side effects. The second therapy was more tolerable, but Jennifer's fatigue and mobility issues seemed to increase rapidly over the next year. Worsening depression and anxiety, combined with increased physical symptoms, led to more hospital and doctor visits, an inability to work, and a couple of additional prescriptions to manage her mental health. Jennifer finally switched to a third MS treatment option, which appeared to slow disease progression. Although Jennifer gradually adapted to managing her condition, circumstances sometimes took her by surprise, such as when a heat wave exacerbated her MS symptoms and sent her to the emergency room. While at the hospital, Jennifer experienced a dangerous drug interaction because her Electronic Health Record did not reflect the other drugs prescribed by her psychiatrist. After that episode, Jennifer realized she was better informed about her overall health than any of her individual healthcare providers. Unfortunately, only one member of her care team had an electronic patient portal, which reflected only part of her record and offered no way to correct outdated information.

Our Future

When imaging shows that Jennifer has MS, her health care provider orders a precision diagnostic test to identify exactly what subtype of MS Jennifer has. She has a subtype that will likely progress quickly, so her doctor suggests she starts a specific disease-modifying drug right away. Jennifer's genetic results show two therapies are likely to work well, but one is likely to cause severe side effects. Once she starts therapy, Jennifer's fatigue and mobility issues improve. She remains largely stable for the next three years. Although her symptoms don't worsen, a precision monitoring test detects an increase in disease activity. Jennifer and her care team decide to switch to a new, more targeted drug. Although her MS continues to progress, Jennifer can keep working (and avoid major mood disorders) for several years.

As a Californian, Jennifer has access to her unified California Patient Record. When she begins seeing a psychiatrist, Jennifer grants them access to view and update her record, and her new doctor can immediately see her complete health history and enter new medications. A regular digital reminder encourages Jennifer to update medications, health issues, or social history her providers might not know about. Jennifer's care providers also encourage her to use a wearable device and to log her good and bad days online. A disease management application alerts Jennifer to important correlations: her mood symptoms are better when she walks at least 5,000 steps a day, her mobility symptoms are worse when she gets less than 7 hours of sleep, and her fatigue and mental fog are much worse when the temperature exceeds 73 F. Based on sleep logs and the weather forecast, the application notifies Jennifer of days when she might want to manage her energy or environment.

Social Determinants of Health

When a patient visits the doctor, they are rarely asked about their home, school, or work environments; whether they feel safe in their neighborhood; or have access to healthy food and positive relationships. These are some of the elements known as social determinants of health (SDOH). SDOH can affect one's health more than their genetic makeup. By incorporating SDOHs with biological and clinical information, precision medicine considers all aspects of a patient and more effectively prevents or addresses the root causes of health conditions–an approach known as "whole person care."

Case Study: Enrolling in Clinical Trials

Today's Situation

When Uday's doctor diagnosed them with a rare cancer, the doctor told Uday their best bet was to participate in a clinical trial. Uday wasn't certain what this meant. Would they get the real treatment? Was it safe? The trial clinic was a two-hour drive away. Having the costs of their care fully covered appealed to Uday, but the commute to the clinic would be expensive and time-consuming. Thinking it offered the best chance to get better, Uday eventually joined the trial. They faced a cumbersome enrollment process and burdensome protocols. Uday thought some of the check-ins could have been done over the phone or at their local lab, but the trial did not include these options. Even though Uday didn't know if they had received the trial therapy, their cancer responded so well that it seemed worth the hassle. But, Uday was dismayed to realize, when the trial was over a year later, they would not have ongoing access to the long-term maintenance drug, which was not yet approved for use outside of trials. Uday did not even know how the trial had gone: Would the drug be approved? How long would that take? What could be done in the meantime to stop the cancer from returning?

Our Future

When Uday first accesses their California Patient Record, the system asks them to confirm that their primary care physician, other members of the care team, and any emergency medical staff can access their records as needed for treatment. It also explains that their medical data can help researchers prevent and treat disease. The California Patient Record then walks them through a brief, clear consent process that explains the risks and some example uses, then asks which kinds of data they are willing to share, and whether they want to be notified when their data have been used in a study. After their cancer diagnosis, Uday gets notified about a study for a new treatment. The benefits and risks seem clear, and it looks like only a couple of office visits are needed. They go through the online consent process and enroll, then get the first study questionnaire, which can also be completed online. As the study progresses, Uday gets the occasional progress update from the researchers and study coordinator through their California Patient Record, so they feel like part of the team. They continue to do online check-ins. After office visits, Uday and their regular doctor can see the blood tests and scan results in their record. Although Uday does not know if they are in the placebo arm of the study, their cancer is moving toward remission. At the end of the study, Uday is informed that they were on the trial drug and is offered the chance to continue taking it, provided they continue to share data about their experiences. When the results are published, Uday gets a notice that includes a short summary of the study's findings, as well as a link to its publication, which they can read without having to pay for access to the journal in which it appeared.

How are data used for precision medicine?

Precision medicine uses data at a number of different scales. On a massive scale, data from tens or even hundreds of thousands of people can be studied to find associations that would be statistically impossible to see otherwise. On a very small scale, hundreds of thousands of data points can be collected about just one patient to customize their care, in the form of DNA sequencing or digital images. An important part of precision medicine is data stewardship, which means that researchers and health care providers are responsible for ensuring that data are accurate, used ethically and in the correct circumstances, and protected.

What is an Electronic Health Record?

An Electronic Health Record, or EHR, is the digitized version of a patient's medical chart. It contains all the information a provider has collected for a patient, including diagnoses, test results, x-rays, procedures, and prescriptions. Digitization of health records make them searchable and easier to share among care teams. Researchers can also use EHRs to easily find possible study participants.

When clinicians have more information, they can create a clearer picture of their patients and provide them with more precise care.

Ideally, an EHR would contain information from sources other than doctors' offices, clinics, and hospitals. Other possible data sources include: clinical trials or research experiments in which a patient has participated; personal electronics like fitness trackers, smartphones, and smart watches; direct-to-consumer genetic tests from companies like 23andMe and Ancestry.com; and census data.

Is my health data safe?

The U.S. government enacted the Health Insurance Portability and Accountability Act of 1996 (HIPAA) Privacy Rule to make sure you have rights over your own health information, no matter what form it is in. Data used in research undergoes a process to remove identifying information (such as name, date of birth, and address) from a dataset so that it cannot be traced to specific individuals.

Whether patient health information is in an EHR, on paper, or in other media, providers have responsibilities for safeguarding the information by meeting the requirements of federal and state health data privacy and security laws.

HIPAA Rules protect patient health information held by providers and give patients certain rights with respect to that information. This set of regulations includes:

  • the Privacy Rule, which ensures the privacy of identifiable patient information;
  • the Security Rule, which sets national standards that prevent data leaks or hacking of electronic protected health information; and
  • the Breach Notification Rule, which obligates providers to notify patients following a breach of unsecured health information.

To further facilitate health data privacy, the US government enacted the Genetic Information Nondiscrimination Act (GINA) of 2008, which prohibits discrimination in the workplace because of one's genetic characteristics. California extended these protections beyond the workplace by passing CalGINA in 2011.

Additional Resources

Want to learn more about precision medicine? Check out our Educational Resources page for an extensive list of talks, webinars, workshops, white papers, and more.

Want to know more about California's current efforts to advance precision medicine? Subscribe to our newsletter, explore our archived news, and browse the California Precision Medicine Asset Inventory to see what's happening across the state.

For More Information

Julianne McCall, PhD
Julianne McCall is Co-Director of the California Initiative to Advance Precision Medicine at OPR.