Medications, vomiting, smoking and acid reflux cause a temporary bitter taste in the mouth, according to Michael Shaffer and Catherine Spader of Better Medicine. Long-term smoking and mouth, nose or head injuries can lead to permanent distortion of a person's sense of taste.
A persistent bad taste in the mouth is known as dysgeusia, as Shaffer and Spader explain. When something interferes with the mouth's normal taste process, a person experiences a change in his sense of taste. The taste process involves sensory neurons found in the taste buds and the olfactory system. These neurons send signals to the brain about the foods a person tastes. A bitter taste often results from smoking and injuries, diseases or conditions that interfere with the taste process. Certain conditions, such as vomiting, only cause a temporary bitter taste, while autoimmune and neurological disorders and chemical poisoning lead to more serious and longer-lasting taste problems.
According to New Health Guide, the most common cause of bad taste is taking medications, like antibiotics. Tooth decay and other health problems that affect the taste buds also lead to a bitter taste in the mouth. A person is also likely to experience bitter taste due to acid reflux, a condition wherein acids in the stomach rise up to the esophagus, causing a foul breath.