Chlorophyll is the compound in plants that makes them green. According to a 2011 monograph written by Rebecca Bramwell, Pharm D, and peer-reviewed and published by NaturalStandard.com, a research and review collaboration group for alternative medicine, chlorophyll is related to protoheme, the pigment that makes your blood red. It's traditional uses include treatment for bad breath and body odor, but it may have other uses.
All green plants contain chlorophyll, but only plants that are safe to eat are used to produce chlorophyll for a supplement. According to "Natural Standard," it's obtained from broccoli, Brussels sprouts, cabbage, lettuce, spinach, chlorella algae, spirulina algae, wheat grass, alfalfa, damiana, nettle and parsley. It's available as a dietary supplement and may be combined with other natural substances.
Chlorophyll is often used to treat bad breath, but according to "Natural Standard," that use is only supported by anecdotal evidence. However, it may be helpful for other conditions. It may be able to help your liver remove toxins. "Natural Standard" also says chlorophyll may be used to treat herpes simplex, also known as cold sores, and benign breast disease, tuberculosis and rheumatoid arthritis.
Chlorophyll supplements are not standardized, so efficacy of any product cannot be established. Product preparation may vary for each manufacturer, so you may not be able to compare one brand to another. According to "Natural Standard," 100 mg chlorophyll two or three times per day is recommended anecdotally for bad breath. Doses of 100 mg three times per day for up to four months have been used in a study on protection against aflatoxins.
According to the University of Maryland Medical Center, allergic reactions are possible if you take chlorophyll supplements. You may develop a photosensitive rash if you're allergic to it. The U.S. FDA does not regulate chlorophyll or any other dietary supplements for effectiveness or amounts of active ingredients, so don't take chlorophyll supplements without speaking with your doctor first.