Antacids
Neutralize existing stomach acid. The bowel side effect tells you which one it is.
Antacids neutralize acid that is already in the stomach for fast, short-term relief of heartburn and indigestion. The key test points are their bowel effects and drug interactions.
- Aluminum hydroxide
- Bowel effect: Constipation · Also binds phosphate (used in CKD)
- Magnesium hydroxide (MOM)
- Bowel effect: Diarrhea · Avoid in renal failure (magnesium builds up)
- Aluminum + magnesium (Maalox, Mylanta)
- Bowel effect: Balanced · Combined to offset each other's bowel effect
- Calcium carbonate (Tums)
- Bowel effect: Constipation · Excess → rebound acid, hypercalcemia
Antacids change stomach pH and bind many medications, reducing their absorption. Give other oral medications at least 1 to 2 hours apart from antacids. This is a common interaction question.
"Aluminum makes you constipated, magnesium makes you go." Aluminum → constipation; Magnesium → diarrhea. Combination products (Maalox, Mylanta) blend both so the effects cancel out.
Every key point in this guide fits on one free printable page. Jump to the free cheatsheet PDF →
H2 Receptor Antagonists
The "-tidine" drugs. Reduce acid production (less than PPIs).
H2 blockers block histamine-2 receptors on stomach cells, reducing acid secretion. They are used for GERD, ulcers, and heartburn.
- Famotidine (Pepcid): the commonly used H2 blocker today. Take before meals or at bedtime.
- Cimetidine (Tagamet): many drug interactions (inhibits liver enzymes) and can cause confusion in older adults — used less often.
- Note: ranitidine (Zantac) was removed from the U.S. market over an NDMA contamination concern.
Less potent than PPIs, but useful and available over the counter. Watch for confusion in older adults, especially with cimetidine.
Famotidine, cimetidine — the "-tidine" ending is an H2 blocker (reduces acid). Don't confuse with the "-prazole" PPIs, which suppress acid more strongly.
Proton Pump Inhibitors (PPIs)
The "-prazole" drugs. The strongest acid suppression — take before meals.
PPIs block the final step of acid production (the proton pump), giving the most powerful and longest-lasting acid suppression. Used for GERD, peptic ulcers, H. pylori, and erosive esophagitis.
- Examples: omeprazole (Prilosec), pantoprazole (Protonix), esomeprazole (Nexium), lansoprazole.
- Timing: take 30 to 60 minutes before the first meal. Do NOT crush or chew delayed-release capsules.
- Long-term risks: low magnesium, low B12, reduced calcium absorption (fracture risk), increased C. difficile risk, and rebound acid when stopped. Use the lowest effective dose for the shortest time.
PPIs only block pumps that are active, so they work best taken before a meal (30–60 min before breakfast), not after. Pantoprazole is the common IV PPI for hospitalized clients. Remember "-prazole = proton pump."
Antiemetics
Stop nausea and vomiting — each class has its own signature warning.
- Ondansetron (Zofran)Chemo, post-op, general N/V
- 5-HT3 blocker. Watch QT prolongation; headache and constipation common.
- Metoclopramide (Reglan)Gastroparesis, N/V (prokinetic)
- Boxed warning: EPS / tardive dyskinesia — report abnormal movements.
- Promethazine (Phenergan)N/V, motion sickness
- Sedating; give deep IM or diluted IV slowly (severe tissue damage if it leaks out of the vein).
- Scopolamine (patch)Motion sickness
- Anticholinergic — dry mouth, blurred vision; apply behind the ear; wash hands after.
Metoclopramide can cause extrapyramidal symptoms and tardive dyskinesia (tremors, restlessness, rigidity, repetitive face/tongue movements), which may be permanent. Report any abnormal movements immediately, especially in older adults or with long-term use.
Antidiarrheals
Slow the gut — but not when the diarrhea is infectious.
- Loperamide (Imodium): slows intestinal motility; OTC.
- Diphenoxylate/atropine (Lomotil): opioid-related; the atropine discourages misuse.
Antidiarrheals are contraindicated in infectious diarrhea (e.g., C. difficile, other bacterial causes). Slowing motility traps the pathogen and its toxins, which can worsen the infection and cause toxic megacolon. Avoid them with bloody diarrhea, high fever, or a known infection — and always replace fluids and electrolytes.
Laxatives
Four main types — and one (lactulose) does an extra job in liver failure.
- Bulk-formingPsyllium (Metamucil)
- Take with a full glass of water (can cause obstruction if taken with too little fluid). Safest for routine use.
- Stool softenerDocusate (Colace)
- Softens stool; good for preventing straining (post-op, cardiac, post-MI).
- OsmoticPolyethylene glycol (MiraLAX), lactulose, magnesium citrate
- Pull water into the bowel. Lactulose also lowers ammonia in hepatic encephalopathy.
- StimulantBisacodyl (Dulcolax), senna
- Short-term only — long-term use causes dependence and loss of normal bowel tone.
Besides treating constipation, lactulose lowers blood ammonia by trapping it in the bowel for excretion — that's why it's used in hepatic encephalopathy. The goal there is 2–3 soft stools per day (too many = dehydration).
Mucosal Protectants & H. pylori Therapy
Protect the ulcer, and treat the bacteria that causes most of them.
- Sucralfate (Carafate): coats and protects the ulcer. Take on an empty stomach (1 hour before meals and at bedtime); give other drugs 2 hours apart (it binds them). Most common side effect: constipation.
- Misoprostol (Cytotec): a prostaglandin that prevents NSAID-induced ulcers. Contraindicated in pregnancy — it causes uterine contractions and miscarriage.
- H. pylori "triple therapy": a PPI plus two antibiotics (commonly clarithromycin + amoxicillin) for 10–14 days. Finish the full course to fully clear the bacteria.
Misoprostol can cause miscarriage and is contraindicated in pregnancy. A woman of childbearing age must have a negative pregnancy test and use reliable contraception before and during therapy.
Administration Timing & Key Teaching
"When do I take it?" is one of the most tested GI med concepts.
- PPI (omeprazole, pantoprazole)
- 30–60 minutes before the first meal
- Sucralfate
- On an empty stomach, 1 hour before meals + at bedtime
- Antacids
- After meals for relief; 1–2 hours apart from other drugs
- Bulk-forming laxative
- With a full glass of water
- H2 blocker
- Before meals and/or at bedtime
Other High-Yield Points
- Antacids and sucralfate both bind other drugs — separate doses.
- Don't crush or chew delayed-release PPI capsules.
- Report abnormal movements with metoclopramide; report black/tarry stools (possible GI bleed) on any of these.
- Replace fluids and electrolytes with vomiting or diarrhea.
PPIs and sucralfate are taken before meals/on an empty stomach; antacids are taken after meals for relief. Mixing these up is a classic test trap.
? A client is prescribed omeprazole and sucralfate. When should each be given relative to meals?
Frequently Asked Questions
Common student questions on this topic.
When should antacids be taken in relation to other medications?
When should a proton pump inhibitor (PPI) be taken, and what are the long-term risks?
Why shouldn't antidiarrheals be used for infectious diarrhea?
What is the major warning with metoclopramide (Reglan)?
Why is misoprostol contraindicated in pregnancy?
How should sucralfate (Carafate) be taken?
Quick-Reference Cheatsheet
Every key point from this guide on a single printable page.
Gastrointestinal Medications Cheatsheet
Free, printable PDF · no spam · returning visitors skip the email step.