7 Bile Acid Sequestrant Interactions You Should Know About

If you’re living with high cholesterol, many medications can help you maintain your health alongside a nutritious diet and routine exercise. Bile acid sequestrants (BAS) are no exception; they’re some of the oldest and safest medications used to lower cholesterol.

Bile acids themselves are molecules made by the liver to help with digestion. BAS medications work by attaching to bile acids in the gut. This forces the body to use up extra cholesterol to make new bile acids. Colestipol (Colestid), colesevelam (Welchol), and cholestyramine (Prevalite, Locholest) are key examples. They’re sometimes used as alternatives to statin medications, like atorvastatin (Lipitor). 

Unfortunately, they aren’t totally free from side effects. These sticky molecules can also bind to things that aren’t bile acids — like other medications. This may prevent your medication from working like it’s supposed to. Notably, colesevelam seems to have fewer interactions than other BAS medications.

1. Narrow therapeutic index medications like warfarin

Certain medications have a narrow therapeutic index (NTI). This means that small changes in medication levels in the body can cause big changes in tolerability. NTI medications are especially sensitive to drug interactions.

The blood thinner warfarin (Coumadin, Jantoven) is an example of a NTI medication. For this reason, people who take warfarin require regular blood tests to make sure their dose is safe and effective.

BAS medications can decrease warfarin’s absorption. This makes warfarin less effective and increases the risk for a blood clot. To prevent this, it’s recommended to take warfarin at least 1 hour before or 4 hours after your BAS.

There are many other medications that are also considered to be NTI medications. Other examples include: 

• Digoxin (Lanoxin)

• Lithium (Lithobid)

• Phenobarbital 

• Theophylline (Elixophyllin, Theo-24)

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BAS medications bind to these medications as well, possibly harming their effectiveness. But the risk is lower for colesevelam compared to the other BAS drugs.

2. Thyroid medications like levothyroxine

Levothyroxine (Levoxyl, Synthroid, others) is an important medication for people living with hypothyroidism (an underactive thyroid). It helps maintain healthy levels of thyroid hormone. These hormones do a lot to make sure the body uses energy correctly. 

Taking a BAS at the same time as thyroid medications, like levothyroxine, lowers how much thyroid hormone is available. BAS drugs bind to thyroid medications and prevent them from being absorbed. This can dampen their effectiveness and cause hypothyroidism symptoms — such as fatigue, weight gain, or feeling overly cold — to reappear.

You should separate your BAS and thyroid medication by at least 4 hours.

3. Birth control pills

Birth control pills are the most popular way to prevent unwanted pregnancies, among other uses.

As mentioned previously, BAS drugs like to bind to other medications when they’re in your gut at the same time. Unsurprisingly, this includes birth control pills. When these medications interact, it lowers the amount of birth control medication that can be absorbed by the body. This increases the risk of unintended pregnancy or side effects from changing hormone levels. 

For this reason, try to separate your birth control pill and BAS by at least 4 hours. 

4. Certain antibiotics

Antibiotics are life-saving medications that are used to treat infections caused by bacteria. They’re not the right medication for every infection or ailment, but they’re a go-to for many bacterial infections, like urinary tract infections (UTI). 

As with other medications, a BAS can bind to antibiotics. This prevents them from getting absorbed into the body. Because of this, they can’t fight infections as effectively. The risk is lower with colesevelam compared to the others, but an interaction is still possible.

There are a couple antibiotics that may interact with BAS medications. One example are tetracyclines, including tetracycline (Achromycin V) and doxycycline (Doryx, Vibramycin, others). Penicillin is another example.

5. Sulfonylureas like glipizide

Sulfonylureas are medications that treat Type 2 diabetes. They include medications like glipizide (Glucotrol XL), glimepiride (Amaryl), and glyburide (Diabeta, Glynase).

Some BAS medications — like colesevelam — can also help control blood glucose (sugar) for people with Type 2 diabetes. But when taken around the same time, the BAS binds to the sulfonylurea. The interaction lowers its effectiveness, which can raise blood glucose levels. 

It’s a good idea to separate sulfonylureas and a BAS by at least 4 hours.

6. Vitamins

Vitamins are an important part of life. They keep the body healthy by providing the building blocks for some of its basic functions.

All vitamins can be broken down into two basic types. Water-soluble vitamins are absorbed, used, and removed by the body quickly. Fat-soluble vitamins are absorbed with fats in the diet and stay in your body for longer. Both of these vitamin types can be eaten in the diet or taken as supplements, like multivitamins.

BAS medications bind easily to fat-soluble vitamins in your body. So there is a risk that you could experience lower levels of these vitamins while taking a BAS. Fat-soluble vitamins include:

• Vitamin A

• Vitamin D

• Vitamin E

• Vitamin K

Folic acid is a water-soluble vitamin, but it also interacts with BAS.

To avoid potential complications, people who need to take a vitamin supplement and BAS should separate them by at least 4 hours.

7. Mycophenolate

Mycophenolate (CellCept) and mycophenolic acid (Myfortic) are crucial medications for those who need them. If you’ve had an organ transplant, they can help prevent your body from rejecting the transplant. Missing even a few doses of these medications can be serious.

When a BAS binds to mycophenolate, it lowers the amount of medication that can be absorbed. This makes it less effective. That means there is an increased risk an organ transplant could be unsuccessful.

When should I contact my healthcare provider about a bile acid sequestrant interaction?

If you’re taking a BAS, you should speak with your pharmacist or healthcare provider any time you begin a new medication. Your care team can help prevent medication interactions, avoid unnecessary risks, and keep your health in tip-top shape. It helps if they have an updated list of medications you take, too. They may suggest separating your BAS from potentially interacting medications by at least 4 hours.

A drug interaction can happen even if you’ve been taking your medications for a while. This can be caused by many things, including changes in your diet. If you notice a difference in how a medication works or makes you feel, it might be time to talk to a member of your healthcare team.

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Written by:

Nathan Williams, PharmD, RYT

Nathan is a clinical pharmacist, certified yoga instructor, and medical content writer. His clinical practice has spanned several sub-specialties including: emergency medicine, nutrition, and pediatrics.

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. Ulrich’s experience includes direct patient care in hospital and community pharmacies.

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