Chapter 41

obsessive-compulsive disorder (OCD) A common, chronic and long-lasting disorder in which a person has uncontrollable, reoccurring thoughts (obsessions) and behaviors (compulsions) that he or she feels the urge to repeat over and over.

onlay A dental onlay is similar to a filling and a crown. An onlay extends down the side of your tooth.

oral allergy syndrome (OAS) Where you react to certain fruits and vegetables having proteins related to other substances you are already allergic to, like pollen.

orphan drug An orphan drug is a drug developed to treat rare diseases. To encourage pharmaceutical companies to make them, these drugs are not given the rigorous testing that normal drugs are, .

osteoporosis In osteoporosis, your bones become weak and break easily.