6 Doxycycline Interactions You Should Know About

When you go to your local pharmacy to pick up a new prescription, there’s a chance the pharmacist on duty will ask if you have any questions about your medication. This conversation can take a few minutes, but they just want to make sure you take your medication in the safest way possible. Often, they’ll offer tips on how to avoid or manage potential medication interactions. 

Doxycycline (Vibramycin, Doryx, Oracea) is no exception to this. It’s a popular antibiotic used to treat bacterial infections, Lyme disease, and even acne. It’s relatively affordable, too. But tetracycline antibiotics, like doxycycline, are known to interact with other medications you might be taking. 

6 doxycycline interactions to know about

When doxycycline is combined with other medications, it can affect how other medications are absorbed into your bloodstream. It can also change their exit strategy when leaving your body. This can make other medications more or less effective. Similarly, certain medications can impact doxycycline’s ability to fight an infection. 

With so much variability, it’s good to know about doxycycline’s most common medication interactions before you start taking it. 

Keep in mind: This isn’t a complete list of medication interactions with doxycycline. For a more detailed list, make sure to talk to your pharmacist.  

1. Penicillin antibiotics

Penicillin antibiotics are a group of medications that treat bacterial infections. Common examples are amoxicillin (Amoxil), ampicillin, and penicillin. However, due to differences in how they fight bacteria, doxycycline can interfere with penicillin antibiotics. This makes penicillin antibiotics less effective. 

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Thankfully, this interaction is pretty avoidable. Your healthcare provider likely won’t prescribe them at the same time. However, if you happen to have any unused medications from an old prescription, be sure to dispose of them. Never try to combine antibiotics unless you’re instructed to do so. 

2. Warfarin

Warfarin (Coumadin, Jantoven) is a blood thinner used to treat or prevent blood clots. If you’re given a prescription for doxycycline, combining the two can enhance warfarin’s effects. This can make your blood too thin. This raises your risk of severe bleeding or bruising. 

If you take warfarin, your healthcare provider should check your international normalized ratio (INR) before you start doxycycline. This is a test that measures how thick or thin your blood is. They may also want to check it more frequently while you’re taking doxycycline. This will help make them recommend warfarin dose adjustments as needed. 

3. Barbiturates and antiseizure medications

Barbiturates, phenytoin (Dilantin), and carbamazepine (Tegretol) are prescription medications that can make doxycycline leave your body faster. This can make doxycycline less effective, which could lead to an undertreated infection. 

Examples of barbiturates are phenobarbital and pentobarbital. Barbiturates can be used to help with sleep or control seizures, while phenytoin and carbamazepine are used to control seizures.

Your healthcare provider will likely monitor you closely while taking doxycycline with any of these medications. They could also decide to adjust your medication doses or give you a different antibiotic that avoids this interaction altogether.

4. Antacids

Heartburn is uncomfortable. It’s the burning sensation that happens when the contents of your stomach move up into your esophagus. Over-the-counter antacids can provide quick relief by neutralizing stomach acid that’s causing these symptoms. But they can also affect the absorption of other medications. 

Antacids usually contain aluminum, calcium, or magnesium. These ingredients can block the absorption of doxycycline from your gut. When this absorption is blocked, doxycycline is less effective. 

A few examples of antacids include: 

• Mylanta (aluminum hydroxide/magnesium hydroxide/simethicone)

• Tums (calcium carbonate)

• Milk of Magnesia (magnesium hydroxide) 

• Rolaids (calcium carbonate/magnesium hydroxide)

To avoid this interaction, it’s recommended to take doxycycline 1 to 2 hours before or after taking any antacids.

5. Pepto-Bismol 

If you’re experiencing diarrhea or an upset stomach, you may reach for a bottle of Pepto-Bismol (bismuth subsalicylate). Unfortunately, doxycycline and Pepto-Bismol don’t get along. 

Pepto-Bismol can prevent doxycycline from being fully absorbed from your gut. Like some of the interactions above, this causes doxycycline to be less effective.

If you are taking doxycycline and experiencing stomach discomfort in your stomach or diarrhea, talk to your healthcare provider or pharmacist. They can recommend safe alternative options to Pepto-Bismol.  

6. Iron supplements

If you have low iron levels, your healthcare provider may recommend an iron supplement. Iron supplements are available as stand-alone products, but they’re also a common ingredient in multivitamins. Regardless of the form, iron can prevent the absorption of doxycycline.

You can avoid this by planning ahead. When taking multivitamins, be sure to check if the product contains iron. Plan to take doxycycline 2 hours before or 3 hours after taking iron or any iron-containing medications. 

How can I avoid or manage potential interactions with doxycycline?

Documentation and communication are the best ways to avoid and manage interactions. Always provide an updated list of the medications you currently take to your healthcare provider and pharmacist. If you don’t like the idea of maintaining a list, medication reminder apps are another option to consider.

If you think you’re experiencing a medication interaction, contact your healthcare provider as soon as you can. As mentioned above, interactions can impact a medication's effectiveness or usefulness. This can cause issues down the line if not addressed. 

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Written by:

John Maneno, PharmD

John Maneno, PharmD, is a licensed pharmacist and freelance writer. He completed a 2-year fellowship program with Belmont University and Aegis Sciences Corporation where he served as an instructor for biomedical literature evaluation and intro to drug information and informatics courses.

Edited by:

Joshua Murdock, PharmD, BCBBS

Joshua Murdock, PharmD, BCBBS, is a licensed pharmacist in Arizona, Colorado, and Rhode Island. He has worked in the pharmacy industry for more than 10 years and currently serves as a pharmacy editor for GoodRx.

Reviewed by:

Austin Ulrich, PharmD, BCACP

Austin Ulrich, PharmD, BCACP, is a board-certified ambulatory care clinical pharmacist. In his early career, he provided direct patient care in a variety of settings, including hospital and community pharmacies, and in a primary care clinic as a clinical pharmacist.

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