immediate release
Imagine dropping a sugar cube into hot tea: it dissolves all at once and the sweetness arrives quickly. An immediate-release dosage form behaves the same way — once swallowed, it breaks apart and dissolves rapidly, handing over essentially its whole dose in a short time so the drug can be absorbed without delay.
Technically, immediate release is the default, unmodified behaviour of a tablet or capsule: there is no special coating or polymer designed to slow things down. A disintegrant helps the tablet crumble, the powder wets and dissolves, and the dissolved drug is then free to cross the gut wall. Most pharmacopoeial dissolution tests for these products expect a large fraction (often 80% or more) released within 30 to 45 minutes.
The trade-off is that blood levels rise quickly and then fall, so a short-acting drug may need dosing several times a day. Immediate release is the reference point against which all modified-release products are designed and compared; it is not inferior, simply the baseline.
A standard 500 mg paracetamol tablet is an immediate-release form, releasing most of its drug within minutes to give rapid pain relief.
The everyday baseline against which slower forms are measured.
An immediate-release product is not the same as a fast-dissolving or orodispersible tablet; the latter is engineered to disintegrate even faster, sometimes on the tongue.