Berberine or its salts or derivatives are identified as the active compound for selectively inhibiting lung cancer, potentially without toxic side effects. Berberine is preferably obtained by synthesis or partial synthesis, or is obtained from natural sources, such as Coptis teeta, or other berberine containing plants. Berberine and its derivatives are also active against HIV, and may be a safe new drug for the prevention of AIDS, alone or in combination with other antiviral agents. Composition and method of inhibiting tumor or viral infections and malaria without toxic side effects. A natural composition from the rhizome of Coptis teeta may be used as a safe new drug for the prevention of human breast cancer.