There is a lack of consensus on the safety of the coadministration of drugs and red blood cells (RBCs). A systematic review was undertaken to establish the evidence base for this question and assess how the evidence may be translated into present clinical day practice. Comprehensive searches of MEDLINE, EMBASE, CINAHL, the Cochrane Library and hand searching of transfusion journals, guidelines and websites identified 12 relevant papers: 11 in-vitro experiments and 1 case report. Data on incidences of haemolysis and agglutination following coadministration were extracted and analysed. Overall findings suggest that iron chelators (two papers), antimicrobials (three papers) and lower doses of opioids (three papers) are safe to coadminister with RBCs. Haemolysis was observed with higher doses of opioids (three papers). Transposition of these findings to clinical practice is limited because of the lack of clinical applicability of in-vitro experiments and diversity in how, and what, clinical outcome measures were used. Further evidence from true clinical settings would be required to inform clinical practice on the efficacy and safety of the coadministration of drugs and RBCs.