Patent protection for an invention is valid for 20 years from the application's filing date. There are however some cases where you can can apply for an extended period of five years of protection. Especially for patents for medicinal products and plant protection products, the term of protection can be extended by up to five years. This extension is called a Supplementary Protection Certificate (SPC).
When a patents validity has expired the SPC protection may begin. The SPC covers the active compound/compounds that are protected by the patent.
SPC is common when it comes to patents in the pharmaceutical sector and extends the duration of the patent in order to compensate the patent owner for the time between patent filing and and when the product is authorized for sale, which usually is a long time and complex procedure