Complex sentence: In the mid- 1990s, fentanyl was introduced for palliative use with the fentanyl patch, followed in the next decade by the introduction of the fentanyl lollipop, dissolving tablets, and sublingual spray which are absorbed through the tissues inside the mouth.
Split into simpler sentences: In the mid- 1990s, fentanyl was introduced for palliative use in the form of patch. This was followed in the 2000s by the introduction of a lollipop, dissolving tablets, and sublingual spray which are absorbed through the tissues inside the mouth.