A lot of everyday medicines pass into breast milk only in tiny amounts and are considered compatible with breastfeeding. Paracetamol and many antibiotics, for example, are commonly used by breastfeeding parents. However, some drugs do reach the baby in meaningful amounts or can affect milk supply, so blanket reassurance is not safe.
Whenever you are offered or buy a medicine, tell the prescriber or pharmacist that you are breastfeeding. They can check reliable resources and often choose a version that is well studied in breastfeeding. Timing a dose right after a feed can sometimes further reduce what reaches the baby.
Avoid stopping a medicine you genuinely need without advice, and avoid assuming herbal or over-the-counter products are automatically safe. If your baby seems unusually sleepy, poorly feeding, or unwell after you start a new medicine, contact a healthcare professional.