microencapsulation can be used to slow the release of a drug into the body. this may permit one controlled release dose to substitute for several doses of non-encapsulated drug and also may decrease toxic side effects for some drugs by preventing high initial concentrations in the blood. there is usually a certain desired release pattern. in some cases, it is zero-order, i.e. the release rate is constant. in this case, the microcapsules deliver a fixed amount of drug per minute or hour during the period of their effectiveness. this can occur as long as a solid reservoir or dissolving drug is maintained in the microcapsule.