Why Marinol Drug Interactions Matter

Marinol (Dronabinol) is processed by your liver and affects your brain and cardiovascular system. That means it can interact with a wide range of other medications — sometimes in ways that are dangerous. Knowing what to watch for can help you stay safe while getting the benefits of your treatment.

This guide covers the most important Marinol drug interactions, including prescription medications, over-the-counter products, supplements, and even certain foods.

How Drug Interactions Work With Marinol

Dronabinol is broken down in your liver by two enzymes: CYP2C9 and CYP3A4. Medications that speed up or slow down these enzymes can change how much Dronabinol is in your bloodstream at any given time.

• Enzyme inhibitors slow the breakdown of Dronabinol → more drug stays in your system → stronger effects and more side effects
• Enzyme inducers speed up the breakdown → less drug in your system → reduced effectiveness

Beyond liver enzymes, Marinol also interacts with anything that affects your central nervous system, heart rate, or blood pressure.

Prescription Medications That Interact With Marinol

CNS Depressants (High Risk)

These medications cause drowsiness on their own. Combined with Marinol, sedation can become severe or dangerous:

• Benzodiazepines — Alprazolam (Xanax), Diazepam (Valium), Lorazepam (Ativan)
• Opioid pain medications — Oxycodone, Hydrocodone, Morphine, Fentanyl
• Barbiturates — Phenobarbital
• Sleep medications — Zolpidem (Ambien), Eszopiclone (Lunesta)

If you take any of these, your doctor needs to know before starting Marinol.

CYP2C9 Inhibitors

These drugs slow down Dronabinol metabolism, increasing its effects:

• Amiodarone — a heart rhythm medication
• Fluconazole — an antifungal medication

CYP3A4 Inhibitors

These also increase Dronabinol levels in your blood:

• Ketoconazole — antifungal
• Ritonavir — HIV protease inhibitor (commonly used in HIV treatment)
• Clarithromycin and Erythromycin — antibiotics

This is especially important for HIV patients who may be taking Ritonavir-based antiretroviral therapy and Marinol simultaneously. Your doctor may need to adjust doses.

CYP2C9 and CYP3A4 Inducers

These speed up Dronabinol breakdown, potentially making it less effective:

• Rifampin — antibiotic used for tuberculosis
• Phenobarbital — seizure medication
• Carbamazepine — seizure and mood stabilizer

Anticholinergic Agents

Medications with anticholinergic effects can combine with Marinol to cause additive tachycardia (rapid heartbeat) and drowsiness. Examples include certain bladder medications, muscle relaxants, and older antihistamines.

Sympathomimetic Agents

Stimulant medications like amphetamines (Adderall) can combine with Marinol to cause additive increases in heart rate and blood pressure.

Tricyclic Antidepressants

Drugs like Amitriptyline and Nortriptyline can cause additive drowsiness and rapid heartbeat when combined with Marinol.

Blood Thinners

Warfarin (Coumadin) is highly protein-bound, and Dronabinol may displace it, potentially increasing bleeding risk. If you take Warfarin, your doctor should monitor your INR levels closely after starting Marinol.

Disulfiram and Metronidazole

This interaction applies only to Syndros (the liquid form of Dronabinol), which contains alcohol. Taking Syndros with Disulfiram or Metronidazole can cause a severe reaction including nausea, vomiting, flushing, and headache. This combination is contraindicated.

Over-the-Counter Medications and Supplements

Antihistamines

Common allergy and cold medications like Diphenhydramine (Benadryl), Cetirizine (Zyrtec), and Doxylamine (NyQuil ingredient) can increase drowsiness when taken with Marinol.

Herbal Supplements

Some supplements can affect the same liver enzymes that process Dronabinol:

• St. John's Wort — a CYP3A4 inducer that may reduce Marinol's effectiveness
• Valerian root, Kava — may increase sedation
• CBD products — may compete for the same metabolic pathways and increase Dronabinol levels

Always tell your doctor about supplements, even if they seem harmless.

Food and Drink Interactions

Alcohol

This is the most important one. Alcohol is a CNS depressant, and combining it with Marinol significantly increases drowsiness, dizziness, and impaired judgment. Avoid alcohol while taking Marinol.

Grapefruit Juice

Grapefruit and grapefruit juice inhibit CYP3A4, which can increase Dronabinol levels in your blood. Avoid grapefruit while taking Marinol, or talk to your doctor about it.

High-Fat Meals

Eating a high-fat meal before taking Marinol can increase how much of the drug your body absorbs. This isn't necessarily dangerous, but it can intensify side effects. Be consistent with how you take your dose relative to meals.

What to Tell Your Doctor

Before starting Marinol, give your doctor a complete list of:

• All prescription medications you take
• Over-the-counter medications (including allergy pills, sleep aids, and pain relievers)
• Herbal supplements and vitamins
• CBD or cannabis products you use
• How much alcohol you typically drink

Update this list whenever something changes. Even a new antibiotic or antifungal prescribed by a different doctor could interact with Marinol.

If you're looking for a prescribing doctor who can review your full medication list, see our guide on finding a Marinol provider near you.

Final Thoughts

Marinol is an effective medication, but it interacts with a long list of common drugs, supplements, and foods. The good news is that most interactions are manageable — your doctor just needs to know what you're taking so they can adjust doses or monitor you appropriately.

Don't assume something is safe just because it's over-the-counter or "natural." When in doubt, ask your pharmacist or doctor. For more on Marinol, check out our guides on side effects, how it works, and how to save money on your prescription.