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Diphenoxylate Hydrochloride (Lomotil, Lonox, Lomanate)
Revised: May 29, 2023
Published: October 17, 2005

(For veterinary information only)

The size of the tablet/medication is NOT an indication of a proper dose. Never administer any drug without your veterinarian's input. Serious side effects or death can occur if you use drugs on your pet without your veterinarian's advice. 

It is our policy not to give dosing information over the internet.

Brand Name: Lomotil, Lonox, Lomanate

Available in 2.5 mg tablets or as oral liquid


Intestinal motility refers to the ability of intestinal muscle to contract and move intestinal contents from the mouth end of the animal to the anal end.

Years ago, it was thought that diarrhea was the result of excessive motility in the intestinal tract and that intestinal contents were rushed through prematurely in a sequence of muscular spasms. For years, diarrhea was symptomatically treated with medications designed to abolish intestinal muscle tone with the idea that these spasms could be prevented. The results were disappointing.

More recently, the details of intestinal contractions have been elucidated. There are many types of muscle contractions in the intestine. There is the forward-propelling peristaltic contraction that moves intestinal contents forward. There is the segmental contraction that can divide the intestine into small segments where different materials can be sequestered temporarily for absorption and digestion. There is also an overall general muscle tone or tonus to the intestinal tract, and it is this tonus that controls the speed by which intestinal contents move.  More muscle tone/tonus means slower movement of intestinal contents, more absorption of water from the intestinal contents, and less tendency towards diarrhea. When this muscle tone is abolished, intestinal contents simply pour through the tract, and diarrhea is worse.

How this Medication Works

Despite its inability to produce recreational euphoria, diphenoxylate hydrochloride is actually a member of the opiate class of drugs.  (A small amount of atropine is added to diphenoxylate to discourage abuse for recreational purposes; at recommended doses, the atropine causes no effects, but if one tries to use larger quantities, the atropine produces unpleasant symptoms.)  Opiates have numerous effects that have made them beneficial - as well as targets of abuse -  for centuries; one such beneficial effect is an increase in general muscle tone of the small intestine. As described above, increasing tonus means more absorption of water and nutrients and less diarrhea.

Loperamide is a similar drug and may be preferable for dogs as it is believed to have a faster onset of action and lasts longer. Definitive studies are lacking.

Side Effects

Side effects are not common with diphenoxylate hydrochloride, but constipation and/or bloating are possibilities. Since diphenoxylate hydrochloride is an opiate, tranquilization is a possible side effect. None of these effects are considered serious. Cough suppression can be considered a side effect or a desired effect, depending on the patient's condition.

Interactions with Other Drugs

Opiates should not be given to patients concurrently taking L-Deprenyl (Anipryl®) or other Monoamine Oxidase Inhibitors (MAOIs), including tick control products containing amitraz. Actually, serious reactions have only been observed between L-Deprenyl (a monoamine oxidase inhibitor) and meperidine (an opiate), but, to be safe, the warning has been extended to all opiate/monoamine oxidase inhibitor combinations.

Tranquilizers and antihistamines should not be used with opiates as sedating properties may be overly enhanced.

Concerns and Cautions

Use of this medication may falsely elevate lab tests for pancreatitis (amylase and lipase levels).

It should be stored at room temperature in light-resistant containers.

This medication is contraindicated for diarrhea involving intestinal toxins (parvovirus enteritis or patients with liver failure are good examples).  In these cases, the absorption-enhancing effects of diphenoxylate hydrochloride could be a serious problem as one would not want to enhance the absorption of intestinal toxins.

Diphenoxylate hydrochloride should not be used in debilitated patients. Caution is recommended for patients with Addison's disease, increased intracranial pressures, hypothyroidism, liver disease, or severe kidney insufficiency.

It may be given with or without food. If a dose is accidentally skipped, do not double up on the next dose instead, give the dose when it is remembered and time the next dose accordingly.

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