Medicines to Avoid During Pregnancy

Some medicines have a clear risk of malformation, foetal toxicity or neonatal harm and are avoided in pregnancy and in anyone who could conceive without highly effective contraception. Many have safer alternatives; where none exists, treatment is a specialist risk-benefit decision with documented counselling.

Avoidance is not stopping everything. Abrupt withdrawal of antiepileptics, antipsychotics, antidepressants, anticoagulants and corticosteroids can be more harmful than continuation. Replace rather than simply stop.

Highest-risk exposure windows. Weeks 5 to 10 after the last menstrual period for structural malformation (neural tube by week 6); second and third trimesters for renal, ductal, bone, dental and neonatal effects.

Contraception. Anyone taking a known teratogen needs pregnancy testing before starting and highly effective contraception (implant, intrauterine device, injectable, or sterilisation), with repeat testing at intervals.

Unplanned exposure. Date the pregnancy by ultrasound, record dose and timing, assess against the table, consult teratology information, and offer a detailed scan at 18 to 22 weeks. Exposure alone is rarely a reason to end a pregnancy.

Herbal and traditional products. Counsel against unlabelled herbal preparations; pennyroyal, black cohosh, blue cohosh, high-dose ginseng, liquorice in large amounts and many local uterotonic or hepatotoxic products are unsafe.

Highest-risk groups. Anyone who could conceive and is taking valproate, retinoids, thalidomide analogues, mycophenolate, methotrexate or leflunomide. These require a documented pregnancy prevention plan.

Interactions of concern. Enzyme-inducing drugs reduce hormonal contraception and implant efficacy; rifampicin and efavirenz lower etonogestrel exposure, so use a copper or levonorgestrel intrauterine device or medroxyprogesterone acetate injection. Teratogen plus alcohol, khat or tobacco compounds foetal risk.

Special groups.

• Adolescents and unplanned pregnancy: higher rates of unintended exposure; prescribe teratogens only with a negative pregnancy test and contraception.
• Kidney and liver impairment: high-risk drugs (methotrexate, mycophenolate) accumulate; avoid.
• Breastfeeding: avoid cytotoxics, ergotamine, amiodarone and radioiodine; most other items are managed by individual review.
• Regional: easy over-the-counter access to misoprostol, diclofenac and herbal products, and traditional abortifacient use, require direct questions at each visit.

Monitoring. Urine or serum pregnancy test before each teratogen prescription and every 4 weeks (retinoids, thalidomide analogues) or as the local programme directs. Review contraception at every visit. Anomaly scan at 18 to 22 weeks after any exposure.

Stopping rules. Stop ACE inhibitors, angiotensin receptor blockers, retinoids, methotrexate, mycophenolate, leflunomide, warfarin and statins when pregnancy is recognised, after replacing with a safe option. Do not stop antiepileptics, lithium, antipsychotics, anticoagulation for mechanical valves or corticosteroids abruptly; review within 24 to 48 hours with a specialist.

Referral and escalation. Refer any exposure to a known major teratogen the same week to an obstetrician, teratology service or clinical pharmacist, and arrange foetal medicine review. Report exposure outcomes through the local pharmacovigilance system.