Webster's New World Medical Dictionary

levothyroxine sodium
A synthetic thyroid hor-
mone (brand names include: Eltroxin, Levothroid,
Levoxine, Levoxyl, Synthroid) that is used as a thy-
roid hormone replacement drug to treat an under-
active thyroid gland (hypothyroidism). Because not
all brands of levothyroxine sodium are equivalent, it
is important not to switch between brand names or
generic formulations.
LH
Luteinizing hormone.
LHRH
Luteinizing hormone-releasing hormone.
LHRH agonist
A compound that is similar to
luteinizing hormone-releasing hormone (LHRH) in
structure and can act like LHRH.
libido 1
Sexual drive.
2
In psychoanalysis, the
psychic energy from all instinctive biological drives.
library
In genetics, an unordered collection of
cloned DNA from a particular organism (for exam-
ple, an E. coli library, a human DNA library). The
relationships between these clones can be estab-
lished with physical mapping. See also 
genomic
library.
library, genomic
See 
genomic library.
lice, head
See 
head lice.
licensed practical nurse
See 
nurse, licensed
practical.
lichen planus
A common skin disease that fea-
tures small, itchy pink or purple spots on the arms
or legs. The abnormal areas on the skin in lichen
planus are typically flat-topped (hence the term
planus), itchy, and frequently have a polygonal or
angular shape. Lichen planus can occur anywhere
on the body but is characteristically found on the
wrists, shins, lower back, and neck. Lichen planus
on the scalp may lead to hair loss. The causes
of lichen planus are unknown. However, it can be
triggered by the use of certain drugs, such as thi-
azide diuretics, phenothiazines, and antimalarials.
Treatment involves use of topical corticosteroids. In
most cases, the disease spontaneously regresses 6
months to 2 years after onset.