At an age when breastfeeding is the optimal nutritional support for infants, oral drug delivery can be challenging. In the past, the concept of drug delivery during breastfeeding was developed as a means to address challenges in low-income countries by facilitating administration using solid dosage forms without the need for clean water. Hereby, a silicone nipple shield, containing a formulation inside its teat, is meant to be worn by a mother during breastfeeding, enabling drug delivery to the sucking infant through the flow of human milk. Furthering past research, this doctoral work aimed to investigate novel dosage forms for this application, including a fibrous matrix and a gel formulation, as well as the clinical potential, feasibility, and acceptability of therapeutic delivery during breastfeeding. In a clinical context, a descriptive qualitative study revealed the need for alternative infant oral drug delivery technologies in high-resource settings, and parents' and nursing staff's positive response to the concept of drug delivery during breastfeeding. Findings were supported by the anecdotal evidence of difficulties in infant compliance and accurate dosing, and indicated high relevance for a use case in neonatal intensive care. Formulation investigations included zinc sulphate loaded non-woven fibre mats, and iron sulphate loaded liquid-core alginate hydrogels, using a modified and a commercially available nipple shield design. While full release during breastfeeding simulation was not achieved, both formulations enabled superior delivery of their loaded therapeutic dose compared to previously studied dosage forms. In addition, a clinical feasibility study involving the delivery of vitamin B12 from a commercially available nipple shield during breastfeeding was conducted, supported by a qualitative mixed methods approach. Results illustrated the successful delivery of vitamin B12 to breastfed infants and unanimous maternal advocacy for the availability of therapeutic delivery during breastfeeding in the future.