Some anti‑seizure medicines (ASMs) can make certain types of birth control less effective. This list shows which ASMs may affect birth control and how.
Acetazolamide
| Combined oral contraceptive (COC) | ✔ |
|---|---|
| Progestogen‑only pill (POP) | ✔ |
| Injection | ✔ |
| Implant | ✔ |
| Patch | ✔ |
| Intrauterine device (IUD)** | ✔ |
| Intrauterine system (IUS) | ✔ |
| Emergency contraception (ulipristal acetate/levonorgestrel) | ✔ |
Brivaracetam
| Combined oral contraceptive (COC) | ✔ |
|---|---|
| Progestogen‑only pill (POP) | ✔ |
| Injection | ✔ |
| Implant | ✔ |
| Patch | ✔ |
| Intrauterine device (IUD)** | ✔ |
| Intrauterine system (IUS) | ✔ |
| Emergency contraception (ulipristal acetate/levonorgestrel) | ✔ |
Cannabidiol
| Combined oral contraceptive (COC) | ✔ |
|---|---|
| Progestogen‑only pill (POP) | ✔ |
| Injection | ✔ |
| Implant | ✔ |
| Patch | ✔ |
| Intrauterine device (IUD)** | ✔ |
| Intrauterine system (IUS) | ✔ |
| Emergency contraception (ulipristal acetate/levonorgestrel) | ✔ |
Carbamazepine (enzyme inducer)
| Combined oral contraceptive (COC) | ✘ Reduces contraceptive efficacy |
|---|---|
| Progestogen‑only pill (POP) | ✘ Reduces contraceptive efficacy |
| Injection | ✔ Efficacy does not appear to be affected. Some literature advises ^ frequency of injection and additional contraception |
| Implant | ✘ Reduces contraceptive efficacy |
| Patch | ✘ Reduces contraceptive efficacy |
| Intrauterine device (IUD)** | ✔ |
| Intrauterine system (IUS) | ✔ |
| Emergency contraception (ulipristal acetate/levonorgestrel) | ✘ Reduces contraceptive efficacy |
Cenobamate
| Combined oral contraceptive (COC) | ✘ May decrease hormonal contraceptive efficacy |
|---|---|
| Progestogen‑only pill (POP) | ✘ May decrease hormonal contraceptive efficacy |
| Injection | ✘ May decrease hormonal contraceptive efficacy |
| Implant | ✘ May decrease hormonal contraceptive efficacy |
| Patch | ✘ May decrease hormonal contraceptive efficacy |
| Intrauterine device (IUD)** | ✔ |
| Intrauterine system (IUS) | ✘ May decrease hormonal contraceptive efficacy |
| Emergency contraception (ulipristal acetate/levonorgestrel) | ✘ May reduce contraceptive efficacy |
Clobazam
| Combined oral contraceptive (COC) | ✔ See clobazam additional information |
|---|---|
| Progestogen‑only pill (POP) | ✔ See clobazam additional information |
| Injection | ✔ See clobazam additional information |
| Implant | ✔ See clobazam additional information |
| Patch | ✔ See clobazam additional information |
| Intrauterine device (IUD)** | ✔ See clobazam additional information |
| Intrauterine system (IUS) | ✔ See clobazam additional information |
| Emergency contraception (ulipristal acetate/levonorgestrel) | ✔ See clobazam additional information |
Additional information
No DDI noted on Stockleys, but Dynamed (American source) states may decrease plasma concentration of contraceptives.
Clonazepam
| Combined oral contraceptive (COC) | ✔ |
|---|---|
| Progestogen‑only pill (POP) | ✔ |
| Injection | ✔ |
| Implant | ✔ |
| Patch | ✔ |
| Intrauterine device (IUD)** | ✔ |
| Intrauterine system (IUS) | ✔ |
| Emergency contraception (ulipristal acetate/levonorgestrel) | ✔ |
Diazepam
| Combined oral contraceptive (COC) | ✔ May result in diazepam toxicity. Potential breakthrough bleeding |
|---|---|
| Progestogen‑only pill (POP) | ✔ |
| Injection | ✔ |
| Implant | ✔ |
| Patch | ✔ May result in diazepam toxicity. Potential breakthrough bleeding |
| Intrauterine device (IUD)** | ✔ |
| Intrauterine system (IUS) | ✔ |
| Emergency contraception (ulipristal acetate/levonorgestrel) | ✔ |
Eslicarbazepine (enzyme inducer)
| Combined oral contraceptive (COC) | ✘ Reduces contraceptive levels |
|---|---|
| Progestogen‑only pill (POP) | ✘ Reduces contraceptive levels |
| Injection | ✔ |
| Implant | ✘ May reduce contraceptive efficacy |
| Patch | ✘ Reduces contraceptive efficacy |
| Intrauterine device (IUD)** | ✔ |
| Intrauterine system (IUS) | ✔ |
| Emergency contraception (ulipristal acetate/levonorgestrel) | ✘ Reduces contraceptive efficacy |
Ethosuximide
| Combined oral contraceptive (COC) | ✔ |
|---|---|
| Progestogen‑only pill (POP) | ✔ |
| Injection | ✔ |
| Implant | ✔ |
| Patch | ✔ |
| Intrauterine device (IUD)** | ✔ |
| Intrauterine system (IUS) | ✔ |
| Emergency contraception (ulipristal acetate/levonorgestrel) | ✔ |
Fenfluramine
| Combined oral contraceptive (COC) | ✔ |
|---|---|
| Progestogen‑only pill (POP) | ✔ |
| Injection | ✔ |
| Implant | ✔ |
| Patch | ✔ |
| Intrauterine device (IUD)** | ✔ |
| Intrauterine system (IUS) | ✔ |
| Emergency contraception (ulipristal acetate/levonorgestrel) | ✔ |
Fosphenytoin
| Combined oral contraceptive (COC) | ✘ Reduces contraceptive efficacy |
|---|---|
| Progestogen‑only pill (POP) | ✘ Reduces contraceptive efficacy |
| Injection | ✔ Efficacy does not appear to be affected. Some literature advises ^freq of injection and additional contraceptive |
| Implant | ✘ Reduces contraceptive efficacy |
| Patch | ✘ Reduces contraceptive efficacy |
| Intrauterine device (IUD)** | ✔ |
| Intrauterine system (IUS) | ✔ |
| Emergency contraception (ulipristal acetate/levonorgestrel) | ✘ Reduces contraceptive efficacy |
Gabapentin
| Combined oral contraceptive (COC) | ✔ |
|---|---|
| Progestogen‑only pill (POP) | ✔ |
| Injection | ✔ |
| Implant | ✔ |
| Patch | ✔ |
| Intrauterine device (IUD)** | ✔ |
| Intrauterine system (IUS) | ✔ |
| Emergency contraception (ulipristal acetate/levonorgestrel) | ✔ |
Lacosamide
| Combined oral contraceptive (COC) | ✔ |
|---|---|
| Progestogen‑only pill (POP) | ✔ |
| Injection | ✔ |
| Implant | ✔ |
| Patch | ✔ |
| Intrauterine device (IUD)** | ✔ |
| Intrauterine system (IUS) | ✔ |
| Emergency contraception (ulipristal acetate/levonorgestrel) | ✔ |
Lamotrigine
| Combined oral contraceptive (COC) | Modestly reduces lamotrigine exposure. May affect contraceptive efficacy. Use condoms |
|---|---|
| Progestogen‑only pill (POP) | May increase lamotrigine levels/adverse effects. May decrease contraceptive efficacy (evidence lacking). Use condoms |
| Injection | ✔ May increase lamotrigine levels/adverse effects |
| Implant | May increase lamotrigine levels/adverse effects. May decrease contraceptive efficacy (evidence lacking). Use condoms |
| Patch | Modestly reduces lamotrigine exposure. May affect contraceptive efficacy. Use condoms |
| Intrauterine device (IUD)** | ✔ |
| Intrauterine system (IUS) | ✔ |
| Emergency contraception (ulipristal acetate/levonorgestrel) | Lamotrigine might decrease the effects of levonorgestrel. No interaction documented with ulipristal |
Levetiracetam
| Combined oral contraceptive (COC) | ✔ |
|---|---|
| Progestogen‑only pill (POP) | ✔ |
| Injection | ✔ |
| Implant | ✔ |
| Patch | ✔ |
| Intrauterine device (IUD)** | ✔ |
| Intrauterine system (IUS) | ✔ |
| Emergency contraception (ulipristal acetate/levonorgestrel) | ✔ |
Midazolam (Buccal)
| Combined oral contraceptive (COC) | ✔ |
|---|---|
| Progestogen‑only pill (POP) | ✔ |
| Injection | ✔ |
| Implant | ✔ |
| Patch | ✔ |
| Intrauterine device (IUD)** | ✔ |
| Intrauterine system (IUS) | ✔ |
| Emergency contraception (ulipristal acetate/levonorgestrel) | ✔ |
Oxcarbazepine (enzyme inducer)
| Combined oral contraceptive (COC) | ✘ Reduces contraceptive levels/efficacy |
|---|---|
| Progestogen‑only pill (POP) | ✘ Reduces contraceptive levels/efficacy |
| Injection | ✔ |
| Implant | ✘ May reduces contraceptive levels/efficacy |
| Patch | ✘ Reduces contraceptive levels/efficacy |
| Intrauterine device (IUD)** | ✔ |
| Intrauterine system (IUS) | ✔ |
| Emergency contraception (ulipristal acetate/levonorgestrel) | ✘ Reduces contraceptive levels/efficacy |
Perampanel (enzyme inducer)
| Combined oral contraceptive (COC) | May reduce contraceptive exposure at higher doses (≥12mg). Risk not excluded <12mg |
|---|---|
| Progestogen‑only pill (POP) | May reduce contraceptive exposure at higher doses (≥12mg). Risk not excluded <12mg |
| Injection | ✔ |
| Implant | ✘ May reduce contraceptive levels/efficacy |
| Patch | May reduce contraceptive exposure at higher doses (≥12mg). Risk not excluded <12mg |
| Intrauterine device (IUD)** | ✔ |
| Intrauterine system (IUS) | ✔ |
| Emergency contraception (ulipristal acetate/levonorgestrel) | ✘ Reduces contraceptive efficacy |
Phenobarbital (enzyme inducer)
| Combined oral contraceptive (COC) | ✘ May reduce contraceptive levels/efficacy |
|---|---|
| Progestogen‑only pill (POP) | ✘ Probably reduced contraceptive levels/efficacy |
| Injection | ✔ Efficacy does not appear to be affected. Some literature advises ^freq of injection and additional contraceptive |
| Implant | ✘ May reduce contraceptive levels/efficacy |
| Patch | ✘ May reduce contraceptive levels/efficacy |
| Intrauterine device (IUD)** | ✔ |
| Intrauterine system (IUS) | ✔ |
| Emergency contraception (ulipristal acetate/levonorgestrel) | ✘ Reduces contraceptive efficacy |
Phenytoin (enzyme inducer)
| Combined oral contraceptive (COC) | ✘ Reduces contraceptive efficacy |
|---|---|
| Progestogen‑only pill (POP) | ✘ May reduce contraceptive efficacy |
| Injection | ✔ Efficacy does not appear to be affected. Some literature advises ^freq of injection and additional contraceptive |
| Implant | ✘ May reduce contraceptive efficacy |
| Patch | ✘ May reduce contraceptive efficacy |
| Intrauterine device (IUD)** | ✔ |
| Intrauterine system (IUS) | ✔ |
| Emergency contraception (ulipristal acetate/levonorgestrel) | ✘ Reduces contraceptive efficacy |
Piracetam
| Combined oral contraceptive (COC) | ✔ |
|---|---|
| Progestogen‑only pill (POP) | ✔ |
| Injection | ✔ |
| Implant | ✔ |
| Patch | ✔ |
| Intrauterine device (IUD)** | ✔ |
| Intrauterine system (IUS) | ✔ |
| Emergency contraception (ulipristal acetate/levonorgestrel) | ✔ |
Pregabalin
| Combined oral contraceptive (COC) | ✔ |
|---|---|
| Progestogen‑only pill (POP) | ✔ |
| Injection | ✔ |
| Implant | ✔ |
| Patch | ✔ |
| Intrauterine device (IUD)** | ✔ |
| Intrauterine system (IUS) | ✔ |
| Emergency contraception (ulipristal acetate/levonorgestrel) | ✔ |
Primidone (enzyme inducer)
| Combined oral contraceptive (COC) | ✘ May reduce contraceptive efficacy |
|---|---|
| Progestogen‑only pill (POP) | ✘ May reduce contraceptive efficacy |
| Injection | ✔ Efficacy does not appear to be affected. Some literature advises ^freq of injection and additional contraceptive |
| Implant | ✘ May reduce contraceptive efficacy |
| Patch | ✘ May reduce contraceptive efficacy |
| Intrauterine device (IUD)** | ✔ |
| Intrauterine system (IUS) | ✔ |
| Emergency contraception (ulipristal acetate/levonorgestrel) | ✘ Reduces contraceptive efficacy |
Rufinamide (enzyme inducer)
| Combined oral contraceptive (COC) | ✘ Reduces contraceptive levels and efficacy |
|---|---|
| Progestogen‑only pill (POP) | ✘ May reduce contraceptive efficacy |
| Injection | ✔ Efficacy does not appear to be affected. Some literature advises ^freq of injection and additional contraceptive |
| Implant | ✘ May reduce contraceptive efficacy |
| Patch | ✘ Reduces contraceptive levels and efficacy |
| Intrauterine device (IUD)** | ✔ |
| Intrauterine system (IUS) | ✔ |
| Emergency contraception (ulipristal acetate/levonorgestrel) | ✘ Reduces contraceptive efficacy |
Sodium valproate
| Combined oral contraceptive (COC) | ✔ Some oestrogen-containing birth control pills may moderately lower valproate levels |
|---|---|
| Progestogen‑only pill (POP) | ✔ |
| Injection | ✔ |
| Implant | ✔ |
| Patch | ✔ May moderately lower valproate levels |
| Intrauterine device (IUD)** | ✔ |
| Intrauterine system (IUS) | ✔ |
| Emergency contraception (ulipristal acetate/levonorgestrel) | ✔ |
Stiripentol
| Combined oral contraceptive (COC) | May inhibit metabolism of contraceptive. Adjust contraceptive dose if ^adverse effects |
|---|---|
| Progestogen‑only pill (POP) | ✔ |
| Injection | ✔ |
| Implant | ✔ |
| Patch | May inhibit metabolism of contraceptive. Adjust contraceptive dose if ^adverse effects |
| Intrauterine device (IUD)** | ✔ |
| Intrauterine system (IUS) | ✔ |
| Emergency contraception (ulipristal acetate/levonorgestrel) | ✔ |
Tiagabine
| Combined oral contraceptive (COC) | ✔ |
|---|---|
| Progestogen‑only pill (POP) | ✔ |
| Injection | ✔ |
| Implant | ✔ |
| Patch | ✔ |
| Intrauterine device (IUD)** | ✔ |
| Intrauterine system (IUS) | ✔ |
| Emergency contraception (ulipristal acetate/levonorgestrel) | ✔ |
Topiramate (enzyme inducer at a dose of ≥200mg)
| Combined oral contraceptive (COC) | ✘ May reduce contraceptive efficacy >200mg/day |
|---|---|
| Progestogen‑only pill (POP) | ✘ May reduce contraceptive efficacy |
| Injection | ✔ Efficacy does not appear to be affected if given on time. Some literature advises ^freq of injection. Condom must also be used |
| Implant | ✘ May reduce contraceptive efficacy |
| Patch | ✘ May reduce contraceptive efficacy >200mg/day |
| Intrauterine device (IUD)** | ✔ |
| Intrauterine system (IUS) | ✔ |
| Emergency contraception (ulipristal acetate/levonorgestrel) | ✘ Reduces contraceptive efficacy |
Vigabatrin
| Combined oral contraceptive (COC) | ✔ |
|---|---|
| Progestogen‑only pill (POP) | ✔ |
| Injection | ✔ |
| Implant | ✔ |
| Patch | ✔ |
| Intrauterine device (IUD)** | ✔ |
| Intrauterine system (IUS) | ✔ |
| Emergency contraception (ulipristal acetate/levonorgestrel) | ✔ |
Zonisamide
| Combined oral contraceptive (COC) | ✔ |
|---|---|
| Progestogen‑only pill (POP) | ✔ |
| Injection | ✔ |
| Implant | ✔ |
| Patch | ✔ |
| Intrauterine device (IUD)** | ✔ |
| Intrauterine system (IUS) | ✔ |
| Emergency contraception (ulipristal acetate/levonorgestrel) | ✔ |
Delaying menstruation
- Norethisterone needs to be started three days before the effects can be seen
- Individuals using the combined oral contraceptives may be able to delay a period by taking their active pill daily without a break
- If an individual is taking a progestogen only contraceptive pill, consider switching to a combined oral contraceptive pill if there are no contraindications
- Previous venous thromboembolism (VTE), migraines and uncontrolled hypertension are contraindications to certain oestrogens and progestogens
- Severe obesity, defined as BMI more than 30kg/m2, is a risk factor for VTE. Some oestrogens and progestogens are cautioned or contraindicated in patients at high risk of VTE or in obese individuals
- Taking progestogen-only contraceptive pills back-to-back will not delay a period. Norethisterone and medroxyprogesterone are alternative progestogens that can be used for this purpose
Norethisterone oral tab 5mg TDS licensed (only licensed progestogen)
To start at least 3 days prior to expected period. Can be taken for three to four weeks. Not a contraceptive will need other forms of contraceptives to avoid pregnancy.
Medroxyprogesterone oral tab 10mg TDS (off-label)
For patients with contraindications to oestrogens, such as migraines. This dose has been shown to reduce heavy bleeding, although breakthrough bleeding can occur. Periods usually resume within three days of discontinuing medroxyprogesterone tablets.
Depot medroxyprogesterone acetate (DPMA)
DPMA is injected every 12 weeks and it takes time to start delaying periods. Previous VTE history is not a contraindication to DPMA. No periods are seen in 30% of people during the first three months of treatment with DPMA. This increases to 55% after a year of DPMA treatment. The individual can expect their withdrawal bleed to start approximately three days after stopping the pill.
Combined oral contraceptive (COC)
Individuals already taking a COC pill have a withdrawal bleed as opposed to a menstrual period. They can delay their withdrawal bleed by taking their packets back-to-back depending on the type of pill. Breakthrough bleeding is more common in the first few months.
Monophasic 21-day pills
Take the pill for 21 days and start a new packet of pills straight away without a seven-day break. Monophasic pills can be taken continuously for as long as the individual wants, but the risk of breakthrough bleeding increases with prolonged continuous use.
Everyday pills
Take the active pill for 21 days and then miss out the seven inactive pills. Start a new packet of active pills straight away. Advise individuals to dispose of the seven inactive pills safely.
Phasic pills
If the individual is using a biphasic or triphasic contraceptive pill, they should finish the first pack and then start the last phase of pills from the next pack immediately. Advise individuals to dispose of the unused pills safely.
Transdermal patches
Transdermal patches- are usually applied for three weeks, followed by a one week “off” period to mimic the menstrual cycle. These can be applied continuously to delay a withdrawal bleed. This use is off-label. Using the contraceptive patch in an extended regimen has been shown to be equally as effective at delaying a withdrawal bleed as continuous use of the combined oral contraceptive pill.
Last reviewed: 10 March 2026