Effervescent antacids may also contain aspirin, sodium carbonate, or tartaric acid. These products are sold as antacids to neutralize stomach acid and relieve indigestion and heartburn. Gastrointestinal symptoms were epidemiologically associated with use of antacids or cimetidine. Medications associated with constipation include opioids, certain antacids, calcium channel blockers, and anticholinergics. This imbalance can also occur with use of antacids or laxatives that contain magnesium. Treatment includes medications such as antacids, H2 blockers, or proton pump inhibitors. Some medications such as tetracyclines and antacids can decrease absorption of iron. Medications include antacids, H receptor blockers, proton pump inhibitors, and prokinetics. Antacids containing aluminium or magnesium ions inhibit the absorption of moxifloxacin. Medications used may include antibiotics, antacids, loperamide, teduglutide, and growth hormone. Antacids and simple analgesics do not usually relieve the pain. Common examples of drugs that work in this way are antacids and laxatives. Over-the-counter medications for neutralizing acids (antacids) and acid suppressants (H-2 blockers) may be used. Bismuth found in many antacids may turn stools black as may activated charcoal. Consumption of antacids, antiperspirants, vaccines, and cosmetics provide possible routes of exposure.