Compro is a prescription rectal suppository used to control severe nausea and vomiting in adults. Its active ingredient is prochlorperazine, a medication that belongs to a class of drugs called phenothiazines. It works by blocking chemical signals in the brain that trigger the urge to vomit.
How Compro Works
Your brain has a specific area called the chemoreceptor trigger zone that detects toxins or other signals in the blood and responds by making you feel nauseated. Compro blocks dopamine receptors in this zone, essentially cutting off the “vomit” signal before it takes hold. The drug also acts on the digestive tract itself, calming nerve activity along the gut that contributes to nausea.
Because it affects dopamine and several other chemical pathways broadly, Compro can also cause drowsiness and lower blood pressure. These aren’t its intended effects, but they come with the territory of how the drug operates in the body.
Who It’s For and Who Should Avoid It
Compro is approved for adults with severe nausea and vomiting. It is not approved for children under 2 years old or those weighing less than 20 pounds, and the packaging explicitly states it is not for children. Older adults and people who are frail or underweight typically start at the lowest possible dose and increase gradually, since they’re more prone to side effects like drops in blood pressure and involuntary muscle movements.
You should not use Compro if you are heavily sedated or have consumed large amounts of alcohol, opioids, or barbiturates. People with bone marrow problems or anyone who has previously had a serious reaction to a phenothiazine medication (such as jaundice or blood cell abnormalities) should avoid it as well.
The FDA requires a boxed warning on this medication: elderly patients with dementia-related psychosis who take antipsychotic drugs face a significantly higher risk of death. In clinical trials, the death rate in drug-treated patients was about 4.5% over 10 weeks, compared to 2.6% with a placebo. Most of these deaths were cardiovascular or infection-related. Compro is not approved for treating dementia-related psychosis.
Dosage and How to Use It
The standard adult dose is one 25-milligram suppository twice a day. Because it’s a rectal suppository, Compro is particularly useful when nausea is too severe to keep an oral medication down. You can generally expect it to start working within 30 to 60 minutes after insertion.
Elderly patients and those in weakened condition are usually started at the lower end of the dosing range and monitored closely. Your doctor will adjust the dose based on how well it controls your symptoms and whether you experience side effects.
Side Effects
The most common side effects reflect Compro’s broad activity in the brain and nervous system. Drowsiness is frequent, and drops in blood pressure (especially when standing up quickly) can cause dizziness or lightheadedness. Some people experience dry mouth, constipation, or blurred vision from the drug’s effects on nerve signaling.
The more concerning side effects involve involuntary muscle movements. These can include muscle stiffness, restlessness, tremors, or unusual movements of the face and tongue. These reactions are more common in older adults and tend to appear with higher doses or longer use. If you notice any unusual or uncontrollable movements, that warrants prompt medical attention because some of these changes can become permanent with continued use.
Drug Interactions to Know About
Compro amplifies the effects of anything else that slows down your central nervous system. Alcohol, opioid painkillers, antihistamines that cause drowsiness, and sedatives all become stronger and longer-lasting when combined with this medication. The combined sedation can be dangerous.
If you take blood pressure medication, Compro can interfere. Certain diuretics may worsen the blood pressure drops it causes, while some blood pressure drugs may become less effective. Compro can also lower the seizure threshold, which matters if you take anti-seizure medications, as your dose may need adjusting. It can reduce the effectiveness of blood thinners and increase blood levels of certain heart medications like propranolol.
How Compro Compares to Oral Prochlorperazine
Prochlorperazine is available in oral tablets and as an injection, but Compro specifically refers to the rectal suppository form. The active drug is the same. The suppository form exists because severe nausea and vomiting often make swallowing and keeping down a pill impossible. The onset time is similar across forms, roughly 30 to 60 minutes, though individual response varies. Your doctor may choose the suppository when oral medications aren’t practical or when vomiting is too persistent for a pill to stay down long enough to absorb.