Cimetidine (H2 blocker), Omerprazole (proton pump inhibitor), Misoprostol (synthetic prostaglandin), Sucralfate, Aluminum Hydroxide, and Sodium Bicarbonate are used to treat heartburn, ulcers, gastroesophageal reflux disease (GERD), and conditions where the stomach produces too much acid, such as Zollinger-Ellison syndrome. Over-the-counter cimetidine is used to prevent and treat symptoms of heartburn associated with acid indigestion and sour stomach. Cimetidine is also used sometimes to treat stress ulcers, hives and itching, and viral warts, and to prevent aspiration pneumonia during anesthesia. Side effects include headache, diarrhea, dizziness, drowsiness, breast enlargement, confusion, excitement, depression, nervousness, hallucinations. Omerprazole can also cause swelling of face, throat, tongue, lips, eyes, hands, ankles, lower legs, difficulty breathing, or hoarseness. Misoprostol may also cause bloody vomit or bloody, tarry stools. Sucralfate side effects include passing red or black stools, coughing up or vomiting material that is bright red or looks like coffee ground

Dicyclomine is used to treat the symptoms of irritable bowel syndrome. Dicyclomine (anticholinergics) relieves muscle spasms in the gastrointestinal tract by blocking the activity of a certain natural substance in the body. Dicyclomine side effects: dry mouth, upset stomach, vomiting, constipation, stomach pain, gas or bloating, loss of appetite, dizziness, tingling, h/a, drowsiness, weakness, blurred vision, double vision, difficulty urinating, hot flushed, dry skin, confusion, forgetfulness, hallucinations, unsteadiness, coma, anxiety, excessive tiredness, difficulty falling asleep or staying asleep, excitement, inappropriate mood, muscle weakness, rapid or pounding heartbeat, fainting, hives, skin rash, itching, or difficulty breathing or swallowing.

Bismuth Subsalicylate is used to treat occasional upset stomach, heartburn, nausea, and ulcers caused by Helicobacter pylori. It is also used to treat diarrhea. It works by helping to slow the growth of bacteria that might be causing the diarrhea. Side effects are rare but can include darkening of tongue and/or stools.

Vomiting is the forceful expulsion of contents of the stomach and often, the proximal small intestine. It is a manifestation of a large number of conditions, many of which are not primary disorders of the gastrointestinal tract. Regardless of cause, vomiting can have serious consequences, including acid-base derangements, volume and electrolyte depletion, malnutrition and aspiration pneumonia.

A deep breath is taken, the glottis is closed and the larynx is raised to open the upper esophageal sphincter. Also, the soft palate is elevated to close off the posterior nares. The diaphragm is contracted sharply downward to create negative pressure in the thorax, which facilitates opening of the esophagus and distal esophageal sphincter. Simultaneously with downward movement of the diaphragm, the muscles of the abdominal walls are vigorously contracted, squeezing the stomach and thus elevating intragastric pressure. With the pylorus closed and the esophagus relatively open, the route of exit is clear.

This is a good explanation of how we vomit. An important question is what causes us to vomit? There are bilateral centers in the medulla that initiate the actions listed above that we will call the vomitting center (VC).

VC gets input from:

(1) the chemoreceptor trigger zone (CTZ) in the area postrema

(2) from visceral afferents, especially from the GI tract as well as from other organs (eg, heart, bile ducts and ureters), and from

(3) extramedullary portions of the brain (eg, vestibular and olfactory systems).

Area postrema: If you inject a dye that does not penetrate the blood brain barrier (BBB), it will stain only a tiny portion of the brain lying under the floor of the fourth ventricle that is called the area postrema. This indicates that the BBB is more penetrable in this area and this allows the body an important protection mechanism. After toxins are ingested, they circulate throughout the body. The brain needs to be able to detect these toxins to initiate vomitting so that further absorption does not occur. The CTZ within the area postrema senses these emetogenic stimuli and then sends excitatory signals to the vomitting center. Chemotherapy agents, anesthetics, and metabolic disturbances (such as diabetic ketoacidosis and uremia) may trigger vomitting at the CTZ. Importantly, many of our antinausea medications act here, especially the dopamine and serotonin antagonists (eg, phenothiazines and 5HT3 antagonists like ondansetron (Zofran)).

The vestibular system: When there is a vestibular component to nausea and vomitting, anticholinergic agents (eg, scopolamine patch) or an antihistamine (eg, an H-1 blocker like meclizine (antivert)) may be prescribed.

Chemotherapeutic agents or their metabolites can directly activate the medullary chemoreceptor trigger zone.

Dopamine antagonists – such as prochlorperazine which is a phenothiazine act by blocking dopamine receptors. 

5HT3 antagonists – ondansertron, selectively block 5HT3 receptors in the peripheral visceral vagal afferent fibers and in the chemoreceptor trigger zone of the brain.

Metoclopramide – in one of several substituted benzamides with antiemetic activity.  Antidopaminergic side effects such as sedation, diarrhea, and extrapyramidal symptoms limit its high dose use. Metoclopramide has peripheral cholinergic (eg, increases GI motility and GE sphincter tone) and central antidopaminergic effects (effective at CTZ).

Corticosteroids – dexamethasone and methylprednisolone are effective against mildly to moderately emetogenic chemotherapy. The mechanism of their action is not known

Cannabinoids – including dronabinol and nabilone are effective against moderately emetogenic chemotherapy. They are seldom the first line antiemetics

Aprepitant – is a substance P/neurokinin 1 receptor blocker

Increased motility of the GI tract and decreased absorption of fluid are major factors in diarrhea. Antidiarrheal drugs include antimotility agents, adsorbents, and drugs that modify fluid and electrolyte transport.

Antimotility agents: Two drugs that are widely used to control diarrhea are diphenoxylate and loperamide. Both are analogs of meperidine and have opioid-like actions on the gut, activating presynaptic opioid receptors in the enteric nervous system to inhibit acetylcholine release and decrease peristalsis. At the usual doses, they lack analgesic effects. Side effects include drowsiness, abdominal cramps, and dizziness. Because these drugs can contribute to toxic megacolon, they should not be used in young children or in patients with severe colitis.

Adsorbents: Adsorbent agents, such as bismuth subsalicylate, methylcellulose, and aluminum hydroxide are used to control diarrhea. Presumably, these agents act by adsorbing intestinal toxins or microorganisms and/or by coating or protecting the intestinal mucosa. They are much less effective than antimotility agents. They can interfere with the absorption of other drugs.

Agents that modify fluid and electrolyte transport: Bismuth subsalicylate, used for traveler's diarrhea, decreases fluid secretion in the bowel. Its action may be due to its salicylate component as well as its coating action.

Here is the definition of constipation from the Mayo Clinic's website -- Constipation is infrequent bowel movements or difficult passage of stools. Constipation is a common gastrointestinal problem. What's considered normal frequency for bowel movements varies widely. In general, however, you're probably experiencing constipation if you pass fewer than three stools a week, and your stools are hard and dry.
Constipation may be treated by a variety of laxatives from several different categories.

Irritants and stimulants: Senna is a widely used stimulant laxative.

Bulk laxatives:The bulk laxatives include hydrophilic colloids. They form gels in the large intestine, causing water retention and intestinal distension, thereby increasing peristaltic activity. Similar actions are produced by methylcellulose, psyllium seeds, and bran. They should be used cautiously in patients who are bed-bound, due to the potential for intestinal obstruction.

Saline and osmotic laxatives:Saline cathartics, such as magnesium citrate, magnesium sulfate, sodium phosphate, and magnesium hydroxide, are nonabsorbable salts that hold water in the intestine by osmosis and distend the bowel, increasing intestinal activity and producing defecation in a few hours.

Stool softeners (emollient laxatives or surfactants: Surface-active agents that become emulsified with the stool produce softer feces and ease passage. These include docusate sodium, docusate calcium, and docusate potassium. They may take days to become effective. They should not be taken together with mineral oil because of the potential for absorption of the mineral oil.

Lubricant laxatives: Mineral oil and glycerin suppositories are considered to be lubricants.