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Information at (866) 626-6847 or visit us online at: www.OTISpregnancy.org.

Phentermine and Pregnancy

The information below will help you determine if your prenatal exposure to phentermine will increase the
fetal risk above the background risk. With every pregnancy, any women has a 3 to 5 percent chance of
having a baby with a birth defect. The information contained in this fact sheet should not be used as a
substitute for the medical care and advice of your health care provider.


What is Phentermine?
Can taking Phentermine make it harder for
Phentermine is a medication used as an
me to get pregnant?
appetite suppressant to treat obesity. Women
There is no information about whether
are sometimes prescribed medications such as
Phentermine makes it more difficult for women
Phentermine to assist them in losing weight.
to become pregnant.
Phentermine stimulates the central nervous

system. It is also known as Adipex, Fastin,

Ionamin, and Zantryl.
I took Phentermine for several months but

stopped three months ago. I just found out

I'm two months pregnant. Will my baby be
Is Phentermine the same as Fen-Phen?
ok?
No. Fen-Phen was a medication, made
Your baby was not actually exposed to
of phentermine and fenfluramine, prescribed to
the Phentermine that you took. Although the
help people lose weight. Fenfluramine was
rate at which Phentermine is broken down in
taken off of the market in September 1997
the body varies from person to person, most of
because of the concern that it caused heart
the Phentermine should be gone from a
problems when used. Since then, Fen-Phen has
person's body four to five days after taking the
been unavailable. Phentermine, however,
last dose. Phentermine is well absorbed in the
continues to remain on the market.
body, and the body gets rid of the medication

easily. Therefore, the Phentermine would have

been gone from your body before you became
Is it safe to lose weight while I'm pregnant?
pregnant.
Some medical complications are more

likely in pregnancy if you are significantly

overweight, including gestational diabetes
I've been using Phentermine for the past
(diabetes that develops and lasts only during
month and just found out I'm 2 months
pregnancy) and high blood pressure. Your
pregnant. Is my baby ok?
health
care
provider
can
discuss
There
is
little
information
on
recommendations regarding weight gain and
Phentermine exposures during early pregnancy,
loss during pregnancy, but in general, it is not
but there is some information that looks at
recommended that you lose weight during
women who used Fen-Phen during the first
pregnancy. Some studies suggest weight loss
trimester of pregnancy. This information
during the first trimester of a pregnancy can
shows no increase in the rate of birth defects.
increase the risk for having a baby who doesn't
Furthermore, there was no pattern to the birth
weigh as much as it should, or in some cases, a
defects present. The existence of a pattern in
baby with a neural tube defect.
birth defects is important because if a
Neural tube defects, such as spina bifida, occur
medication were thought to cause birth defects,
when the baby's spine does not close properly.
it would be expected to produce the same birth

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defects consistently. If there is no consistency,
Is Phentermine safe to use while nursing my
then it is not likely the medication is
baby? I gained a lot of weight while I was
responsible.
pregnant. I am thinking of using Phentermine

to lose the weight. Can I still breastfeed my

baby?
I used Phentermine before I knew I was
It is possible for Phentermine to pass
pregnant and am concerned about my baby.
into breast milk, so a baby could be exposed
Are there any tests I could have to make sure
while nursing. We do not know how much
my baby is ok?
Phentermine gets into breast milk, or what
An ultrasound examination can often be
effects it can have on a baby who is breastfed.
used to determine if the baby has physical birth
Because Phentermine stimulates the central
defects. An ultrasound examination, also
nervous system it might cause side effects in
called a sonogram, allows a health care
the baby such as tremors, agitation or decreased
provider to "see" many things, including the
feeding. You should talk with your health care
baby's head and spine. Ultrasound may not be
provider about breastfeeding if taking this
able to pick up all birth defects, however. You
medication.
may also want to talk with your health care

provider about the MSAFP test (maternal

serum alpha fetoprotein test), which can detect
June 2004
many neural tube defects.
Copyright by OTIS,

Reproduced by permission.



Now that I know I'm pregnant, can I stop

taking the Phentermine immediately?

Phentermine has not been associated
References:
with negative side effects when people stop
Aronne LJ. Obesity. Women's Health Issues
taking it immediately. Therefore, a person
1998; 82(1): 161-181.
could stop taking Phentermine at any time.
Hale TW. Medications and Mothers' Milk.
Some
appetite
suppressants,
such
as
1992-2002. Texas: Parmasoft Medical Publishing.
Fenfluramine, need to be slowly stopped over a
Johnson KA, Chambers CD, Dick LM, Felix
RJ, Jones KL. Pregnancy Outcome of Women Exposed
period of several days to avoid negative side
to Fen/Phen. OTIS (Abstract) 1998.
effects. You should, however, talk with your
Jones KL, Johnson KA, Dick LM, et al.:
health care provider before discontinuing any
Pregnancy outcomes after first trimester exposure to
prescription medication.
phentermine/fenfluramine. Teratology 65: 125-130,

2002.
Robert E, Francannet C, Shaw G. Neural Tube

Defects and Maternal Weight Reduction In Early
I've heard Fen-Phen causes heart problems in
Pregnancy. Reproductive Toxicology 1995; 9(1): 57-59.
adults. Will Phentermine do the same to my
Silverstone, T. Drugs and Appetite. 1982.
baby?
New York: Academic Press.
Fenfluramine, as part of Fen-Phen, is
Stein AD, Ravelli ACJ, Lumey LH. Famine,
Third-Trimester Pregnancy Weight Gain, and
thought to cause reversible heart problems in
Intrauterine Growth: The Dutch Famine Birth Cohort
adults. There are no specific studies examining
Study. Human Biology 1995; 67(1): 135-150.
whether Phentermine affects the developing
Winick M. Nutrition, Pregnancy, and Early
baby's heart. The limited available information
Infancy. 1989. Baltimore: Williams & Wilkins.
suggests it would be unlikely for phentermine
to cause these same types of heart defects in
babies exposed during pregnancy.

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