The following is from the AOPA website (URL is restricted to members). If member, go to medical search for disqualifying conditions and you will see this from the source.
These conditions disqualify a person from holding a medical certificate under FAR Part 67. A special issuance (authorization) can be granted in some cases, such as diabetes. A special issuance grants a medical certificate that allows the pilot to fly but may impose some conditions or limitations:
Diabetes mellitus requiring insulin or oral medication,
coronary heart disease,
substance dependence or abuse,
failed Department of Transportation drug test,
disturbance of consciousness or transient loss of nervous system function without satisfactory explanation,
bipolar disorder (manic-depressive psychosis).
The FAA has established specific procedures for medical certification of pilots who have the following conditions.
Cardiovascular: hypertension, angina, angioplasty, bypass, coronary artery disease, stent, arrhythmia, significant murmur, cardiomyopathy, pacemaker, valve replacement or repair.
Diabetes on oral medication, diet, or insulin
Drug or alcohol problems
Gastrointestinal: ulcers, GERD, inflammatory bowel disease, hepatitis.
Immunodeficiency disorders (HIV)
Amputations and paralysis
Neurologic: Loss of consciousness, seizures, paralysis, transient ischemic attacks, cerebrovascular conditions (stroke).
Psychiatric and psychological: attention deficit/hyperactive disorder (ADD/ADHD), psychiatric, psychological, or mental disorders, substance abuse.
Pulmonary/respiratory disease: asthma, pulmonary emboli, spontaneous pneumothorax, sleep apnea.
Kidney stones, renal transplant
Vision: color vision deficiency, glaucoma, monocular vision, intraocular lens implants, cataract surgery, vision acuity refractive procedures.