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.
Curve B is for a partial agonist acting on the same receptor. Agonist. A drug which binds to a receptor and activates it, producing a pharmacological response (contraction, relaxation, secretion, enzyme activation, etc.).