Power or capacity to produce a desired effect; effectiveness.(noun)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "efficacy" in a sentence
"It has been shown to have long-term efficacy, meaning it could be administered in small doses, potentially reducing severity of side effects."
"The rise in efficacy of “Terrorism” is largely from the increased availability in inexpensive but highly effective weapons and equipment."
"More information on the homeopathic treatment of mental illness and more scientific evidence verifying its efficacy is contained in a newly published textbook on the subject, Homeopathy and Mental Health Care: Integrative Practice, Principles, and Research."