Can I ask what medicine you're taking? Do not follow the tin. Start with 4oz and see. Breastfed babies do not drink as much as much as the tin says.
Have you checked that the medicine needs to stop you from bfing?
Have you spoken to anyone about the medicine and breastfeeding? Most medications are fine. Offer small bottles (3/4oz) and make more as needed. Breastfed babies are unlikely to immediately drink the recommended amounts because they will have been used to feeding little and often (if you’ve been feeding on demand)
The quantity comes at the back of the formula :)