It is always a good idea to ask. But there is not much in the patch...just enough to get to the site. I've never had a systemic effect, ie. relief of pain elsewhere with them. And they are small.
When you use a drug orally it gets diluted thru the whole body.
A patch like this will send only a minute amount into the body, while concentrating it locally where the patch is applied. If you apply HEAT like with any patch, you can drive the drug into the blood stream.
The patches work better IMO because when there is inflammation, there is reduced blood circulation too. By using the medication locally you send the med directly to the target, so much less is needed. Some of an orally used drug may never reach the target!
This is why some PTs use dexamethasone in a process called an iontophoresis.
http://www.ptjournal.org/cgi/content/abstract/83/2/161
The principle is similar only much more modest with Salonpas.
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Weezie looking at petunias 8.25.2017
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