Drug-Drug Interaction can be a serious problem, as many diseases are treated with multiple medications. Drug-drug interaction typically occurs when two co-administered medicines use the same biological route of active absorption or elimination or when one of the two drugs acts as an inhibitor or an activator for the elimination route of the other. This can lead to unwanted overdosing of one of the two drugs, causing safety issues, or it can make one of the two drugs ineffective. At Roche, we monitor the potential for drug-drug interaction very early. With assays on all major metabolizing enzymes and active transporters involved in drug absorption, we check whether bioactive substances interfere with major breakdown or distribution processes and can address this issue very early in the value chain.