The cause of fibromyalgia is unknown; however, it is believed to involve a combination of genetic and environmental factors with half the risk attributed to each. The condition runs in families and many genes are believed to be involved.
Agonist: A substance that acts like another substance and therefore stimulates an action. Agonist is the opposite of antagonist. Antagonists and agonists are key players in the chemistry of the human body and in pharmacology.
An agonist is any drug that combines with a receptor and stimulates its activity. 1  The agonist binds with the receptor and is able to initiate a response. 2  Opiate agonists produce an opiate effect by interacting with opioid receptors. 3  An agonist is any drug that combines with a receptor and stimulates its activity.