Marsa has worked as a staff writer for the Los Angeles Times, wrote a nationally syndicated column for the Los Angeles Times about new medical advances, and has been a contributing editor for Ladies’ Home Journal, and Omni. Her writing appears in Discover, Mother Jones, Los Angeles Times Magazine, Los Angeles, Reader’s Digest, Popular Science, Woman’s Day, Financial Times, Utne Reader, Spin and many others.

Marsa specializes in investigative stories, profiles, long form Q & A interviews, and consumer advocacy pieces and has written on a wide range of topics, from the crisis in the nation’s emergency rooms, the dangers of prescription drugs, the gaping holes in the food safety net, the truth about statins, and the middle class uninsured to evolutionary hot spots, environmental toxins, medical philanthropy in Hollywood and the scientists behind the headlines.

Her article "Acid Test" won the 2009 June Roth Memorial Award for Medical Journalism from the American Society of Journalists and Authors, and she’s been the recipient of numerous other honors, including being named Outstanding Teacher of the Year by UCLA Extension’s Writer’s Program.

Marsa is also the author of Prescription for Profits: How the Pharmaceutical Industry Bankrolled the Unholy Marriage Between Science and Business (Scribner), about the corporate takeover of academic research and its disastrous impact on public health.

She is currently working on a documentary, The Acid Chronicles, about the use of psychedelics such as LSD to treat serious psychiatric ills, like obsessive compulsive disorder, post-traumatic stress disorder, alcoholism and drug addiction.

Since 1988, she’s taught journalism, research methods and nonfiction writing in The Writer’s Program at UCLA Extension, and has mentored dozens of students who have gone on to writing careers.

She is also one of the founders of the Independent Writers of Southern California, which is now the region’s largest writers’ organization, served for many years as the West Coast grievance officer for the National Writer’s Union, and is currently co-chair of the awards committee for the American Society of Journalists and Authors.