There are two types of topical skin patches (sometimes called transdermal patches) on the market:

Reservoir Patches are made with 2 elements: the skin contact tape and the absorbent pad.  The absorbent pad can hold a relatively large amount of formula (as much as 1,500 mg on larger patches).  The advantage of a reservoir patch is that it can hold a great variety of fluids so it is compatible with a wide variety of formulas.

Monolythic patches incorporate the active ingredients into the adhesive. The advantage of a monolythic patch is that it can be cut to size to adjust the dose.  The disadvantage is that only a thin layer of the active ingredient is available as most of it is locked up in the adhesive.  This is not a problem for powerful formulas

Both types of patches offer time release of the active ingredients for several hours or days.  They are easy to use and give the user control over when, where and how long to dose. This is often more effective than other methods that tend to give deliver a larger dose over a short period of time.