Scopolamine products to prevent motion sickness are to be placed behind the ear to. One brand name for this product is Transderm-Scop.
I will write below why it is placed behind the ear, but in terms of the Facebook post, it's probably not accurate. In fact, Snopes.com did a 'Fact-Check' article on a similar subject.
Scopolamine is an antimuscarinic medication with strong anticholinergic effects. Anticholinergics are used for a variety of purposes, from motion sickness to pupil dilation (if you ever had your doctor dilate your pupils, it most likely was from an anticholinergic drug such as atropine or tropicamide).
Many drugs have 'anticholinergic' side effects as well. These side effects include:
- Dry mouth
- Urinary retention
- Dry eyes (blurred vision)
Benadryl, perhaps the most commonly used over the counter antihistamine, has relatively strong anticholinergic effects, which is why it makes you tired. Dramamine also has strong anticholinergic effects, which is why it is marketed specifically for motion sickness.
The anticholinergic effects of drugs are dose dependent, meaning high doses yield greater effects. Very high doses can cause:
- Cardiac abnormalities
- Loss of muscle control
Oral anticholinergic drugs are notorious for their sometimes severe side effects and overdose, either accidental or deliberate, can be extremely serious.
Going back to scopolamine...the anticholinergic effects of the drug are quite effective for preventing motion sickness. The patches go behind the ear not because it is close in proximity to the vestibular system of the inner ear (important for our sense of balance), but because it is one of the more permeable, and consistent trans-dermal absorption areas on our body.
Very small amounts of scopolamine are in the Transderm-Scop patch. It is designed to deliver a total of 1mg over a 72 hours period at a constant rate. With such a small dose, it is important to not have significant deviations in drug absorption.
Overall, the patch was designed to a provide predictable delivery of scopolamine, resulting in in precise plasma concentrations.
In terms of skin permeability, the postauricular area (behind the ear) is the most permeable of any site on the body. This allows very small doses to be used, and reduces the risk of adverse reactions.
Even though the area behind the ear generally provides more predictable drug delivery, there is still significant variation among individuals.
Due to this, the patches have a rate-limiting membrane. This membrane produces a permeation rate that is slower than the skin can absorb (this is based on studies of different human skin types). So the system (and not individual variability of the skin), controls systemic scopolamine delivery.
To summarize, the patches are put behind the ear because:
- Small doses of scopolamine can be used
- The skin behind the ear is the most permeable for trans-dermal absorption and provides the most consistent blood levels of the drug.