Can other medications interfere with birth control pills?

Reviewed by our clinical team

Birth control pills are highly effective, but there is a lot of medicine that affects how the pill works. These can change their effectiveness as contraception. Taking two or more medicines can cause an interaction between them. Having severe diarrhoea or being sick can also affect birth control pills. 

You should be aware of what could cause your hormonal contraception to stop working. In this article we’ll explore the medications and circumstances that can interfere with birth control.  

Why is the contraceptive pill affected by other medicines? 

Many contraceptive pills use oestrogen, progestogen or a combination of the two to prevent you releasing an egg (ovulating). Some medications can cause oestrogen and progesterone levels to drop if you’re taking the pill as well. Certain levels of these hormones are required to prevent ovulation, so lowering these may mean you are no longer protected from pregnancy. 

Enzyme-inducers

The main culprits for causing oestrogen and progesterone levels to drop are enzyme-inducers. These medications speed up the process some contraceptives use to lower levels of hormones in your body. Lowering these levels faster than normal makes them less effective.

A wide range of medications contain enzyme-inducers, conditions that are often treated with enzyme-inductors include:

• Epilepsy
• Depression
• HIV

Enzyme inductors are also often in treatments for:

• Sleep control
• Weight management
• Fungal control
• Some natural remedies 

Which pills are affected by enzyme-inducers?

Both combined and mini pills are impacted by enzyme-inducers. Other hormonal contraceptive methods can also be affected, such as the patch, vaginal ring and implant.

These all use synthetic versions of natural hormones which work together to prevent pregnancy by stopping you releasing an egg (ovulation). This prevents sperm fertilising an egg. 

Contraception methods not affected by enzyme-inducers are the:

• progesterone-only injection
• intrauterine device (IUD)
• intrauterine system (IUS) 

What should I do if I need to take 2 or more medicines?

When you take two medicines at the same time the medicines can interact. This means the effects of one medicine can be altered by the other.

If you have started a new medication speak to your pharmacist, GP or message us in your Patient Record. They’ll let you know if the medication will have an effect on your contraception and whether you need to use additional methods like condoms.

Your alternative contraception may need to be in effect for anything from 7 to 28 days after finishing the medicine that interacts with the pill. 

For long-term treatment, it may be preferable to avoid enzyme-inducing medicines.

You should speak to your doctor or pharmacist before taking any other medicines alongside the pill. This includes herbal and complementary medicines that are available without a prescription. Your GP will be able to provide you with more specific advice and guidance. 

Medicine that may affect the pill

Research into how contraception is affected by medicines is limited. Often there is very little evidence and few direct studies into how individual medicines interact with the pill. Instead, predictions are made by looking at how other drugs interact with hormonal contraception.

Patient information leaflets in medicine packs should let you know of all the potential interactions. Here is a list of medicines that commonly reduce the effectiveness of the pill.   

Which antibiotics affect the pill?

There’s little research into how antibiotics affect the pill especially when it comes to side effects. It’s thought that the side effects of each medication could double up for a worsened effect. However, not everyone will experience side effects such as vomiting and diarrhoea when taking antibiotics.

Most used antibiotics such as amoxicillin, trimethoprim and erythromycin do not affect the pill unless they cause significant diarrhoea or vomiting. If you’re vomiting or have diarrhoea you won’t absorb the pill properly.

The exception is rifampin (used to treat meningitis and tuberculosis) which can lower the effectiveness of the contraceptive pill. Brand names of the medicine include Rifadin, Rimactane, Rifater, Rifamate and IsonaRif.  

Does amoxicillin affect birth control?

No, there’s no scientific evidence that amoxicillin might affect birth control pills. If you experience severe diarrhoea and vomiting for more than 24 hours while taking amoxicillin and the contraceptive pill you won’t be protected from pregnancy.

Ibuprofen and birth control pills

No, ibuprofen doesn’t affect any type of contraception. If ibuprofen makes you sick your pill may not protect you from pregnancy. Follow the advice on your contraception pill packet or information leaflet.  

Morning after pill and birth control pills

The ellaOne version contains a medicine called ulipristal that can temporarily reduce the effectiveness of contraceptive pills for the first 5 days. It’swise to use condoms until your next period. The emergency contraception Levonorgestrel (sometimes branded as Levonelle) should not affect the pill.

Anti-epileptic drugs and birth control pills

The risk of pregnancy is higher in women taking the pill who use anticonvulsants to control seizures, epilepsy, migraines and nerve-related pain. These include phenytoin, oxcarbazepine, carbamazepine, rufinamide, topiramate, phenobarbital, and primidone. Popular branded forms of these medications include Tegretol, Topamax, Dilantin, Trileptal, Mysoline, Luminal, and Solfoton.

Can I take anxiety and sleep control medicines on birth control pills? 

Some AEDs, called barbiturates, are used to control anxiety and sleep disorders, and have been shown to reduce the effectiveness of the pill. These include phentobarbitone, primidone, butabarbital, butalbital, and seco-barbita which have the branded names Luminal, Mysoline and Solfoton.

Can antidepressants affect birth control pills?

Antidepressants like sertraline or citalopram won’t affect birth control pills. However, they can cause diarrhoea. If you experience this side effect for more than 24 hours, read the patient information leaflet of your contraceptive pill for more advice.  

If you start taking antidepressants while using contraceptive pills or vice versa speak to your GP.

Can I take HIV medication and birth control?

Some medicines used to treat HIV and the hepatitis C virus can reduce the effectiveness of hormonal contraception. HIV is spread through unprotected sex, so if you’re taking HIV medication you may want to use condoms.

The most common of these include ritonavir, nelfinavir, nevirapin, norvir, darunavir, lopinavir, fosamprenavir, tripanavir or velfinavir, branded names include Lexiva and Aptius. 

Anti-fungal medication vs birth control pills

Medicine such as griseofulvin used to treat infections like thrush, ringworm and athlete’s foot, can have an impact.

Caffeine and birth control pills

There have been claims that taking caffeine alongside birth control pills can cause side effects like headaches. However, there’s not enough scientific research to say whether this is the case.  

Weight loss medication and birth control pills

The weight loss medicine Orlistat (Xenical), also available over the counter as alli, may theoretically affect absorption of the pill. These medicines induce diarrhoea and therefore reduce the pill’s effectiveness. Additional precautions should be used. 

Natural supplements and the pill

Certain natural supplements don’t mix well with birth control, the main one being St. John’s Wort, which is used for its anti-inflammatory and antidepressant properties. Also known as hypericum, it’s a yellow flower used in herbal remedies, but research has shown that it interacts with oral contraceptives and is likely to increase the risk of unintended pregnancy. 

A 2005 study, published in the journal ‘Contraception’, found that women taking St. John’s Wort daily had 15% less contraceptive hormones in their bloodstream,  increased breakthrough bleeding and increased possibility of ovulation. Pharmacists were told to warn women of the potential interactions and offer non-hormonal replacements.

Research has also highlighted concerns that other herbal remedies such as Vitex, Dong Quai, Red Clover and Black Cohosh could also compromise oral contraceptives.

Conclusion

If you use the contraceptive pill it’s a good idea to be aware of what can and can’t interfere with it. If you’re prescribed a medication by a doctor, you should always mention the contraceptive pill you’re using.  You can also check the patient information leaflet included in your pill pack for advice.  

References

https://www.nhs.uk/conditions/contraception/contraceptive-pill-interact-medicines/
https://www.epilepsy.com/living-epilepsy/epilepsy-and/women/all-women/contraception
https://patient.info/doctor/progestogen-only-contraceptive-pill-pro
https://www.nhs.uk/conditions/contraception/contraceptive-pill-interact-medicines/
https://patient.info/medicine/griseofulvin-for-fungal-infections
https://www.gov.uk/drug-safety-update/st-john-s-wort-interaction-with-hormonal-contraceptives-including-implants

https://www.fsrh.org/standards-and-guidance/documents/ceu-clinical-guidance-drug-interactions-with-hormonal/
https://www.nhs.uk/medicines/sertraline/common-questions-about-sertraline/