A large proportion of drugs available are of little importance in terms of fulfilling primary healthcare needs. Combination drugs increase the risk of side effects, lead to an ineffective dosage and liability to abuse and may also needlessly increase the cost. Drug combinations make it more dif cult to  nd the causative agent responsible for the adverse reactions. In many cases their stability is doubtful, reducing the ef cacy of many preparations. The Fifteenth WHO model list of essential medicines (March 2007) contains only 25 approved  fixed dose combinations, whereas in Nepal, there are innumerable examples of irrational drug combinations, which are easily available and can be bought even without a prescription. A system of screening the drug combinations that are already licensed and available in the market is implemented in many developed and developing countries. Rational combinations can be of immense help to the health care system. These combinations may improve the quality of life for many and increase compliance. But irrational  fixed dose combination products can be equally harmful.