Friar Lawrence has knowledge on potions whose properties seem magical. What would be the implications for a holy man with knowledge of such...

It is, indeed, possible for the Friar to have composed a
potion which slows down the heart beat of a person so much that the individual appears
dead.  In Alexandre Dumas's novel, The Count of Monte Cristo, for
instance, the Count, in an attempt to foil an evil step-mother, induces a death-like
state in a young woman so as to lure the woman into her
room.

Herbs and flowers have long been used--and still are
studied today as possible cures--for their healing and medicinal effects.  Inudations
were even made in medicine in America with the use of herbs.  For instance, when a
doctor could find no successful treatful for a burn victim, he learned from a woman that
tea leaves in water helped to prevent infection. 

The use
of herbs and potions by the Friar serve to point to the importance of moderation rather
than the fateful impetuosity of Romeo and Juliet:

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Oh, mickle is the powerful grace that
lies

In herbs, plants, stones, and their true
qualities.

For naught so vile that on the earth doth
live,

But to the earth some special good doth
give;

Nor aught so good but, strained from that fair
use,

Rvolts from true birth, stumbling on
abuse.

Viture itself turns vice, being misapplied.
(2.3.15-21)