Common
Gastrointestinal: abdominal pain (6%), diarrhea (9%), flatulence (4%), nausea (7%), vomiting (4%)
Neurologic: headache (12%), dizziness (3%)
Neuromuscular and skeletal: arthralgia (3%)

Rare
Gastrointestinal: constipation, dry mouth, hepatitis
Blood problems: low white blood cell count, thrombocytopenia
Immunologic: Stevens–Johnson syndrome, toxic epidermal necrolysis
Metabolic: elevated creatine kinase, elevated cholesterol levels, elevated liver enzymes (AST/ALT), swelling
Musculoskeletal: Muscle disorders, bone fracture and infection, Clostridium difficile infection, osteoporosis-related hip fracture, rhabdomyolysis
Kidneys: interstitial nephritis
Nutrition:  may reduce the absorption of important nutrients, vitamins, and minerals, including certain medications, leaving users at increased risk for pneumonia. Long-term use
Osteoporosis and bone fracture have been observed in people on high-dose and/or long-term (over one year) prescription proton pump inhibitors. Hypomagnesia has been observed in people on medications like pantoprazole when taken for longer periods of time (generally one year or more, although cases have been reported with regimens as short as three months). Deficiencies such as vitamin B12 deficiency, iron deficiency, and calcium deficiency may be seen with long term use. Vitamin B12 deficiency is due to the change in the acidic environment within the stomach with the use of pantoprazole which prevents peptidases from being activated. This prevents the cleaving of R-factor from vitamin B12 and prevents its absorption. Rebound hypergastrinemia may be seen when stopping the medication after long term use. Discontinuation
In people taking PPIs for longer than six months, a dose taper should be considered prior to discontinuation. For those on a moderate to high dose, this can be done by 50 percent every week until on the lowest dose. After a week it can then be stopped.
Diagnosis
Basophilia can be detected through a complete blood count (CBC). The root cause of basophilia can be determined through a bone marrow biopsy, genetic testing to look for genetic mutations, or ultrasound to determine enlargement of the spleen. A bone marrow aspirate may be utilized to confirm an increase in basophils or significantly high numbers of precursors to the granulocytes. Since basophilia is present in a vast range of clinical conditions, depending on a variety of underlying causes, supplemental signs and symptoms must be investigated for a diagnosis. If splenomegaly is detected, a myeloproliferative syndrome may be suspected. Intrinsically related symptoms such as fever, malaise, pruritus (itching) due to the release of histamine, fatigue, and right upper quadrant pain may be present in the afflicted patient. With some conditions, such as polycythemia vera, erythromelalgia, or burning of the palms and soles, coupled with thrombocytosis is common. This severe symptomatology may require urgent attention. If basophilia and the aforementioned symptoms are present with concurrent eosinophilia greater than 1500 cells/μL, hypereosinophilic syndrome may be considered. In cases of underlying allergic reactions or adverse sensitivity, skin rashes may be present.After symptomatic evaluation, a peripheral blood smear is examined in order to determine cell counts.In cases of a supposed myeloid neoplasm, a bone marrow biopsy will be performed utilizing cytogenetic analysis. This type of testing utilizes the karyotypes of chromosomes for each type of leukocyte and looks for a significant abnormality in any of the conventional karyotypes which could support the diagnosis of a neoplastic process.