Webster's New World Medical Dictionary

tendon, Achilles
See 
Achilles tendon.
tendonitis
Inflammation of a tendon (the tissue
by which muscle attaches to bone). Tendonitis most
commonly occurs as a result of injury, as to the ten-
dons around the shoulder or elbow. It can also
occur as a result of an underlying inflammatory
rheumatic disease, such as reactive arthritis or gout.
Sometimes spelled tendinitis.
tenesmus
Straining to defecate or urinate.
Tenesmus refers especially to ineffectual and painful
straining for an extended time. Straining to defecate
is called rectal tenesmus; straining to urinate is
called vesical tenesmus.
tenia
See 
taenia.
tennis elbow
See 
elbow, tennis.
tension 1
The pressure within a vessel, such as
blood pressure (the pressure within the blood ves-
sels).
2
Stress, especially stress that is translated
into clenched muscles and bottled-up emotions.
tension, arterial
See 
arterial tension.
tension, intraocular
See 
intraocular pressure.
tension headache
See 
headache, tension.
teratogen
An agent that can disturb the develop-
ment of an embryo or a fetus. A teratogen is capable
either of terminating a pregnancy prematurely or, if
the pregnancy persists, of damaging the fetus. The
major classes of teratogens include radiation,
maternal infections, maternal metabolic diseases,
chemicals, and drugs. See also 
teratogenic drug.
teratogenic drug
A drug that is capable of acting
as a teratogen and interrupting a pregnancy or
impairing the child. Drugs that are known terato-
gens include, but are not limited to, ACE inhibitors
such as benazepril (brand name: Lotensin), capto-
pril (brand name: Capoten), enalapril (brand
name: Vasotec), fosinopril sodium (brand name:
Monopril), lisinopril (brand names: Zestril,
Prinivil), lisinopril and hydrochlorothiazide (brand
names: Zestoretic, Prinzide), quinapril (brand
name: Accupril), and ramipril (brand name:
Altace); the acne medication isotretinoin (brand
names: Accutane, Retin-A); alcohol, whether
ingested chronically or in binges; androgens (male
hormones); the antibiotics tetracycline (brand
name: Achromycin), doxycycline (brand name:
Vibramycin), and streptomycin; blood-thinners,
such as warfarin (brand name: Coumadin); seizure
medications, including phenytoin (brand name:
Dilantin), valproic acid (brand names: Depakene,
Depakote, Valprotate), trimethadione (brand 
name: Tridione), paramethadione (brand name:
Paradione), and carbamazepine (brand name:
Tegretol); the antidepressant/antimanic drug
lithium (brand names: Eskalith, Lithotab);
antimetabolite/anticancer drugs methotrexate
(brand name: Rheumatrex) and aminopterin; the
antirheumatic agent and chelator penicillamine
(brand names: Ciprimene, Depen); antithyroid
drugs, such as thiouracil/propylthiouracil and car-
bimazole/methimazole; cocaine; the hormone DES
(diethylstilbestrol); and thalidomide (brand name:
Thalomid). Alcohol and illegal or unnecessary
drugs should never be used by women who are
pregnant or who plan to get pregnant. However,
sometimes a medication that is necessary for health
is also a teratogen: thyroid medication, blood thin-
ners, and lithium are a few examples. Female
patients who must take such medications should
work carefully with their physicians to determine
whether an alternative treatment is possible before
and during pregnancy. In some cases the danger of
birth defects is limited to a certain part of the preg-
nancy, and medication can be started again after
that period has passed. Other medications can be
safely restarted upon the baby’s birth.