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.
Other drugs act on the receptor in a blocking role and are antagonists. An antagonist is a molecule that interferes with or prevents the action of the agonist. 2. A contracting muscle that is opposed by contraction of another associated muscle, the antagonist.