Drug interactions and hormonal contraception 

This article was reviewed in August 2026.

With increasing numbers of drugs on the market (e.g. HIV treatments) and the wider uses of existing drugs (e.g.  antiepileptics for migraine and neuropathic pain), we need to be aware of interactions with contraception. This is particularly important because unintended pregnancy in some of these patients may be high risk. 

The College of Sexual and Reproductive Health (CoSRH) produced a clinical guideline on drug interactions with hormonal contraception  in May 2022, which is summarised in this article.

The COSRH emphasises that its guideline should not replace clinical judgement in the management of individual cases. Furthermore, as new drugs are developed and pharmacological research expands, information may quickly become outdated. 

Always check the BNF and use the websites listed in the useful resources box at the end of the article if unsure.

Types of drug interactions

Contraceptive efficacy of hormonal contraceptives may be affected by pharmacokinetic or pharmacodynamic interactions (CoRSH guideline on drug interactions with hormonal contraception). 

Similarly, contraceptives may alter the plasma levels or effects of certain medications. 

Pharmacokinetic interactions: occur where one drug alters the absorption, distribution, metabolism or excretion of another drug – thereby affecting its bioavailability and function. For example, enzyme-inducing drugs (see below). 

Drugs that reduce absorption from the gastrointestinal tract or cause vomiting/diarrhoea can also impact the efficacy of oral contraceptives. 

Pharmacodynamic interactions: occur where one drug has a direct antagonistic or synergistic effect on the clinical function of another. For example, progestogen-only contraception might reduce the efficacy of ulipristal emergency contraception by its opposing action on progesterone receptors. 

Evidence for drug interactions with contraception

There is little direct data showing the impact of drugs on hormonal contraceptive efficacy, or vice versa. The few studies there are involve small numbers of participants – some consisting only of individual case reports. 

The CoSRH has extrapolated from these studies and used known interactions with other drugs to give broad guidance which may be cautious in its approach (CoRSH guideline on drug interactions with hormonal contraception). However, as some drugs are potentially teratogenic, ensuring efficacy is essential to avoid unplanned pregnancy in scenarios where they are used. 

Enzyme-inducing drugs

Why are enzyme-inducing drugs important in contraception?

  • These drugs induce the cytochrome p450 enzyme system in the liver.
  • This enzyme system is the most important family of drug-metabolising enzymes, and metabolises ethinyloestradiol and progestogens into inactive metabolites which are excreted.
  • Enzyme-inducing drugs lead to increased metabolism of concurrent hormonal preparations, which potentially reduces their contraceptive effect. This effect can persist for some time after stopping the drug. 

Note: Drugs that inhibit the cytochrome p450 system (e.g. erythromycin, ketoconazole, sertraline) can reduce the metabolism of hormonal preparations; this may increase blood levels and therefore potentially increase the risk of side-effects. In the case of ethinyloestradiol, it may result in increased risk of VTE. The guideline makes no specific recommendations to adjust the dose of contraception in this situation (CoRSH guideline on drug interactions with hormonal contraception).

Which contraceptives are impacted by enzyme-inducing drugs?

Contraceptives potentially affected by enzyme-inducing drugs Contraceptives NOT affected by enzyme-inducing drugs
  • Combined hormonal contraception (CHC).
  • Progestogen-only pills (POP).
  • Subdermal implant (SDI).
  • Oral emergency contraception (levonorgestrel and ulipristal).

 
  • Intrauterine device (IUD) and all non-hormonal methods.
  • Intrauterine systems (IUS) have a localised effect which is unaffected by liver enzymes.
  • Progestogen-only injectables (POI) as the clearance of depot is roughly the rate of hepatic blood flow, so it is unlikely that its efficacy is reduced with enzyme inducers. This has been supported by studies on depot users taking antiretrovirals.

Common enzyme-inducing drugs

Conditions which should alert us to potential drug interactions with contraception include epilepsy, migraine, HIV, TB, conditions requiring immunosuppressants and severe fungal infection.

The table below includes some of the commoner enzyme-inducing drugs which we may encounter in primary care, but is NOT a comprehensive list of all enzyme inducers (if unsure, check the BNF or one of the other resources listed at the end of the article).

Class of enzyme-inducing drug Examples

Antiepileptics

(note: most antiepileptics have teratogenic potential) 

Carbamazepine

Phenobarbital

Phenytoin

Primidone

Rufinamide

Topiramate (has enzyme-inducing activity at higher (but not lower) doses but, because it is teratogenic, the CoSRH treats it as a potential enzyme inducer, regardless of dose)
Antibacterials

Rifabutin

Rifampicin
Antiretrovirals

Ritonavir 

Ritonavir-boosted protease inhibitors

Efavirenz 

Nevirapine (weak potential interaction – CoSRH clinical guidance: drug interactions between HIV antiretroviral therapy and contraception, 2023) 
Others

St John’s wort

Modafinil (reportedly used off licence as a ‘smart drug’ to improve exam performance)

Contraception counselling and drug history

Before prescribing contraception, we should (CoRSH guideline on drug interactions with hormonal contraception): 

  • Ask about prescribed drugs, over-the-counter ‘herbal’ preparations, dietary supplements and recreational drugs.
  • Check any potential interactions.
  • Remind the patient to inform her usual contraception prescriber if she commences a new treatment because it may interfere with her contraception.
  • Ensure any woman taking potentially teratogenic drugs (e.g. methotrexate, retinoids (Roaccutane), warfarin, most antiepileptics – especially valproate and topiramate) is advised to use highly effective contraception – see below. 

CoSRH advice regarding enzyme-inducing drugs, teratogens and contraceptives

(CoRSH guideline on drug interactions with hormonal contraception)

CoSRH recommendations regarding contraception

Enzyme-inducing +  non-teratogenic Enzyme-inducing +  teratogenic Non-enzyme-inducing + teratogenic
The advice applies if a patient is taking an enzyme inducer or is within 28d of stopping.  
  • Strongly advise either IUD, IUS or POI.
  • ALWAYS advise women on rifampicin and rifabutin to use one of the above methods as these are VERY strong enzyme inducers. The advice below does NOT apply to women on rifampicin or rifabutin.
  • For short-term use (<2m). If the patient wishes to continue her method, she may do so with consistent and careful use of condoms during therapy and for 28d after stopping.

Women on enzyme inducers who wish to remain on CHC:

  • In exceptional circumstances: consider use of a minimum 50mcg (30mcg + 20mcg) monophasic pill during treatment and for a further 28d, with a continuous or tricycling regimen plus pill-free interval of 4d.
  • Counsel about potentially increased risk of VTE.
  • Do not use two patches or two rings in this way.
  • Strongly advise IUD or IUS. POI may be used, but recommend condom use as well.  
  • CHC, POP and SDI NOT recommended. 

 
  • Strongly advise SDI, IUD or IUS.
  • If CHC, POP or POI used, use condoms as well. 

 

Emergency contraception

  • Offer a Cu-IUD.
  • If this is unacceptable/unsuitable, a double dose of levonorgestrel (3mg) can be used.
  • 30mg ulipristal may be used but its efficacy is unknown.
  • Offer Cu-IUD.
  • If unacceptable, choose either 30mg ulipristal or 1.5mg levonorgestrel as per individual requirements. 

MHRA guidance on valproate and topiramate

The MHRA has introduced guidance on the use of valproate and topiramate. It is important to note this applies to MEN as well as women and girls (EMC – valproate: healthcare professionals guide, gov.uk - topiramate (Topamax): introduction of new safety measures, including a Pregnancy Prevention Programme, both accessed 2026). This guidance sits alongside, complements and at times overlaps with the PREVENT Pregnancy Prevention Programme for women/girls of childbearing age. Full details can be found in our associated article Valproate and topiramate: the Pregnancy Prevention Programme.   

CoSRH advice on other drug interactions 

The table below lists some of the important drug interactions relevant to prescribing contraception in primary care, and what actions we need to take (CoRSH guideline on drug interactions with hormonal contraception). This is not a comprehensive list of ALL interactions: if there is uncertainty regarding any interactions, use one of the websites in the useful resources box below to check.   

Drug Contraceptive CoSRH guidance and why
Any drugs which induce severe vomiting/diarrhoea
e.g. Orlistat COC
POP
  • Follow missed pill rules if vomiting occurs within <3h of taking pill or severe diarrhoea occurs for >24h.
  • If persistent diarrhoea or vomiting, consider non-oral method.
  • Recommend consistent use of condoms.
Why? May reduce absorption in the small intestine.
Levonorgestrel 1.5mg 
Ulipristal 30mg

For oral emergency contraceptives:

  • If vomiting occurs within <3h of taking pill or severe diarrhoea occurs for >24h, a repeat dose should be given.
  • If persistent diarrhoea or vomiting, consider Cu-IUD.
  • Recommend consistent use of condoms.
Why? May reduce absorption in the small intestine.
Gastric acid suppressants
Proton pump inhibitors/H2-receptor antagonists/antacids Ulipristal only Use ulipristal with caution if regular use of medicines which suppress gastric acid.
Why? One small study showed that esomeprazole affected levels of ulipristal (albeit a 10mg dose of ulipristal, so impact on efficacy of 30mg not known, nor effect of other drugs that increase gastric pH).
Specific antiepileptics

Lamotrigine

 
  • Use IUS, IUD or POI preferentially.
  • A small study looking at the effect of lamotrigine in women taking a levonorgestrel-based combined pill found reduced progestogen exposure, reduced ovarian suppression and reports of breakthrough bleeding. This suggests that lamotrigine may impact the efficacy of progestogen-containing contraception.
  • The CoSRH concludes that lamotrigine may affect efficacy of CHC, POPs and SDI (although data is lacking), and recommends additional use of condoms if using these methods. These contraceptives may also affect the efficacy of lamotrigine and therefore impact on seizure control (see below).
CHC

 
  • If CHC use is unavoidable, use a continuous regime.
  • Lamotrigine dose may need to be increased and levels checked to ensure efficacy (liaise with specialist regarding this). 
Why? Oestrogen in CHC induces glucuronidation of lamotrigine, leading to reduced drug levels which could result in reduced seizure control during hormonal exposure, or risk of lamotrigine toxicity in hormone-free interval.

POP

SDI

POI

 
  • Counsel about signs of lamotrigine toxicity (dizziness, ataxia, diplopia) in patients starting progestogen-only contraception.
  • Consider monitoring serum lamotrigine levels when the progestogen is stopped (we would probably liaise with a specialist regarding this).

Why? Desogestrel might increase lamotrigine levels (according to one tiny study from 2004 which found that a desogestrel POP caused a 20–100% increase in lamotrigine levels in 7 out 10 women studied.

Evidence relating to effect of other progestogen-only contraceptives on serum lamotrigine levels is extremely limited.

Hormonal preparations 
Ulipristal 30mg CHC
POP
SDI 
POI
IUS
Levonorgestrel 1.5mg

Quick starting:

  • Do not quick start hormonal contraception immediately.
  • Wait 5d before commencing (see article on Quick starting contraception for more information).

Emergency contraception:

  • Ulipristal may be less effective if a progestogen has been used in the previous 7d.
  • Do not give levonorgestrel 1.5mg within 5d of ulipristal.
  • A further dose of ulipristal may be given in the same cycle.
Why? Ulipristal is a progesterone receptor modulator and there is some evidence of an interaction with progestogens.
Thyroxine CHC
  • Consider checking TFTs around 6w after initiation of CHC.
Why? Oral HRT can increase requirement for thyroxine (as it increases thyroid-binding globulin). There is no evidence of a similar effect with COC but theoretically this is possible.
Some potassium-sparing antihypertensives and  potassium supplements 

Diuretics include:

Amiloride

Spironolactone

Avoid drospirenone progestogen-only pill

 

Probably should be cautious with drospirenone-containing combined pills (e.g. Yasmin)

Drospirenone is an aldosterone antagonist with potassium-sparing properties. The concurrent use of potassium-sparing drugs or potassium supplements may increase serum potassium and risk hyperkalaemia. 

 
ACE inhibitors and angiotensin II receptor antagonists 

Could also potentially increase risk of hyperkalaemia if given with drospirenone. 

BUT remember, ACEI/ARBs are also potentially teratogenic medication so we should be cautious prescribing oral contraception in women on these antihypertensives anyway. 
Antifungals 
Griseofulvin

CHC

POP

SDI
  • Use IUC or progestogen-only injectable preferentially.
  • If using oral contraception or the SDI, use condom as well. 
Why? Case reports suggest bleeding pattern changes and unintended pregnancies occurring in women on the COC and griseofulvin. The mechanism is unknown as it is not an enzyme inducer. 
GLP-1 agonists
Tirzepatide

CHC

POP

Remember MHRA advice:

  • Stop tirzepatide and allow a ≥1m ‘washout period’ before trying to conceive (MHRA alert June 2025).

CoSRH advice:

  • Women on oral hormonal contraception should switch to a non-oral contraceptive method, OR use additional barrier contraception, for 4 weeks after starting tirzepatide, and for 4 weeks after any dose increase. (Given the likelihood of multiple dose titrations, it may be more practical to switch to a non-oral method of contraception while taking tirzepatide.)
  • Emergency contraception: there is no direct evidence of the impact of tirzepatide on emergency hormonal contraception. The copper IUD should be offered where appropriate. In women with a BMI >26 or weight >70kg, consider double-dose LNG-EC if this is the patient’s preferred method. 
Why? Tirzepatide has been found in clinical trial data to have a clinically significant effect on the bioavailability of oral contraceptives (CEU-statement-GLP-1-agonists-and-contraception.pdf).
Other GLP-1 drugs No contraceptive limitations.

Remember MHRA advice:

  • Stop semaglutide and allow a ≥2m ‘washout period’ before trying to conceive (MHRA alert June 2025).

CoSRH advice:

  • There is no need to add a barrier method of contraception when using semaglutide, dulaglutide, exenatide, lixisenatide or liraglutide.
  • Follow usual guidance if severe vomiting or diarrhoea occur as a side-effect of these medications.
Why? There is currently no evidence that semaglutide, exenatide, liraglutide, dulaglutide or lixisenatide reduce the effectiveness of oral contraception.

What about antibiotic use and hormonal contraception?

Historical advice

In the past, women were advised to take extra contraceptive precautions when prescribed broad-spectrum antibiotics. This was due to anecdotal evidence of, and theoretical concerns about, drug interactions leading to reduced contraceptive efficacy. 

Current guidance 

Following systematic reviews of all published evidence, the CoSRH (and WHO and US Center for Disease Control) has concluded (on numerous occasions since 2009) that non-enzyme-inducing antibiotics do not impair the effectiveness of hormonal contraception (CoRSH guideline on drug interactions with hormonal contraception). 

Drug interactions and hormonal contraception 

  • A drug history should be part of any contraception counselling, and remember to ask about St John’s wort!
  • Remind patients to inform their doctors if they commence a new treatment because it may interfere with their contraception.
  • Women taking enzyme-inducing medication should be advised to use intrauterine contraception or a progestogen-only injectable.
  • Women taking non-enzyme-inducing teratogens should use intrauterine contraception or a subdermal implant. If pills or injectables are used, advise to use condoms as well.
  • Women on enzyme-inducing teratogens should use an IUD, IUS or progestogen-only injectable PLUS condoms. Pills and the subdermal implant are not recommended.   
  • For emergency contraception, if an IUD is declined, 3mg of levonorgestrel may be given for up to 120h, off licence.
  • Extra precautions are not required when CHC users are prescribed non-enzyme-inducing antibiotics. 

Do you ask about medicines as part of your contraception counselling? 

How many of your patients on enzyme-inducing medication or teratogens are on ‘safe’ contraception?   

Useful resources:

Websites (all resources are hyperlinked for ease of use in Red Whale Knowledge)