Low blood pressure is known medically as hypotension. It often produces feelings of weakness and faintness. The National Heart, Lung and Blood Institute defines low blood pressure as a reading that is below 90 over 60 millimeters of mercury, or 90/60 mmHg. Treatment for hypotension is dependent on its underlying cause. Mild cases that do not cause symptoms may not require treatment.
Medications
A large number of medications can cause low blood pressure and weakness. Drugs prescribed to lower blood pressure are often implicated such as alpha blockers, diuretics, angiotensin converting enzyme inhibitors, angiotensin II receptor blockers, beta blockers and calcium channel blockers. Other drug categories that may be responsible for hypotension include narcotic pain medicines, erectile dysfunction drugs, anti-anxiety drugs, antidepressants, drugs used during surgical procedures and nitroglycerin.
Heart Failure
Moderate to severe heart failure causes low blood pressure and weakness. Other heart conditions such as heart attack, valve problems and low heart rate can also cause hypotension.
Dehydration
Dehydration is responsible for some cases of hypotension and weakness. This may be a chronic condition, such as that found in an elderly person who does not drink enough fluids, or it may be acute, such as in the case of a runner exercising for hours on a hot day without rehydrating. Dehydration can also result from an extended period of vomiting, diarrhea or blood loss.
Severe Infection
A severe infection can significantly lower the blood pressure. One type of infection that often results in hypotension is called septicemia, a life-threatening condition in which an infection has reached the bloodstream.
Thyroid Disorder
MayoClinic.com explains that both an underactive and overactive thyroid gland can cause hypotension. Occasionally, low blood pressure is found to be due to another endocrine imbalance such as low blood sugar or Addison's disease.
Anemia
According to the National Heart, Lung and Blood institute, anemia is responsible for some cases of low blood pressure. It also causes weakness and can be attributed to many different underlying causes.
Pregnancy
MayoClinic.com reports that pregnancy often causes hypotension, as the body prepares for the pregnancy by widening the blood vessels to accommodate a higher blood volume. This pressure change may be more evident when the pregnant woman suddenly rises from a sitting or lying position.
Severe Allergic Reaction
Anaphylaxis is a type of shock associated with a severe allergic reaction. It can bring on significantly lowered blood pressure and other life-threatening symptoms. Certain drugs, food products, latex and bug stings can cause anaphylactic shock in susceptible individuals, reports MayoClinic.com.
