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Q: Hi ( Answered 5 out of 5 stars,   7 Comments )
Subject: Hi
Category: Health > Fitness and Nutrition
Asked by: johnman-ga
List Price: $100.00
Posted: 11 Jul 2005 10:52 PDT
Expires: 10 Aug 2005 10:52 PDT
Question ID: 542217
I have started taking mega doses of phenylalanine (>5gm/day) and I
have noticed a remarkable boost in my libido. There are conflicting
reports on the internet about the safety of Phenylalanine
supplementation. One study in which they gave subjects 5gm/day showed
no adverse effects. There are many websites that state that there are
no known adverse effects from phenylalanine supplementation. Other
websites say that phenylalanine is an excitotoxin and can cause
neurological problems. But this has been shown primarily in invitro
studies of the effects of Phenylalanine on neurons and in infants with
phenylketonuria. My question is whether an ADULT who has an intact
blood-brain barrier and all the necessary enzymes to metabolize
Phenylalanine can take supplementation and if so at what dose?

Subject: Re: Hi
Answered By: nenna-ga on 11 Jul 2005 12:50 PDT
Rated:5 out of 5 stars
Good afternoon johnman-ga  and thank you for the question.

In all the reports I have seen online concerning Phenylalanine (not to
be confused with articles re: aspartame/aparsate), all have stated
that to the normal human being, ingestion of Phenylalanine is not
harmful UNLESS you have penylketonuria (PKU), take certain medications
or take high doses.

PLEASE understand, I am NOT a doctor, nor do I play one on TV,
however, I will state as a friendly warning, because of the potential
for side effects and interactions with medications, ANY dietary
supplement should be taken only under the supervision of a
knowledgeable healthcare provider.  Please contact your family doctor
if you have any more questions.


Phenylalanine is an essential amino acid, which means that it is
essential to human health but cannot be manufactured by the body. For
this reason, phenylalanine must be obtained from food. It is available
in three chemical forms:

1.  L-phenylalanine, the natural form of phenylalanine found in
proteins throughout the body;

2.   D-phenylalanine, a mirror image of L-phenylalanine that is
synthesized in a laboratory (not found in food); and

3.  DL-phenylalanine, a combination of the previous two forms.

The body converts phenylalanine into tyrosine, another amino acid
essential for making proteins, certain brain chemicals, and thyroid
hormones. Symptoms of phenylalanine deficiency include confusion, lack
of energy, decreased alertness, decreased memory, and diminished

Rare metabolic disorder (phenylketonuria, a.k.a PKU) occurs in people
who are missing an enzyme that is needed to properly metabolize
phenylalanine.  People with PKU who digest phenylalanine stand the
chance of developing mental retardation, especially in children.  
Even though children seem to be most highly effected, adults with PKU
will experience mental and intellectual disturbances after an intake
of phenylalanine.

Phenylalanine can be taken as a capsule, powder, or tablet or used as
a topical cream.  Recommended dosages of phenylalanine vary depending
on the health condition being treated. Supplements are recommended 15
to 30 minutes before meals.


According to the National Research Council, the daily recommended
dietary allowances (RDAs) for phenylalanine are as follows:


Birth to 4 months: 125 mg per kilogram of body weight per day 
Children 5 months to 2 years: 69 mg per kilogram of body weight per day 
Children 3 to 12 years: 22 mg per kilogram of body weight per day 

The combination of oral and topical phenylalanine (together with
ultraviolet light) have been used to treat children with vitiligo. The
dose and appropriate length of time to continue the therapy would be
determined by your physician.


Teenagers and adults: 14 mg per kilogram of body weight per day

Some experts suggest that adults may need as much as 39 mg per
kilogram of body weight per day for general health and doses as high
as 50 to 100 mg per kilogram have been used in studies of those with
vitiligo. The most common amounts used range from 750 to 3,000 mg per
day for adults.


Source:  University of Maryland Medical Center

( )

* * * * * * * * * *

"High blood concentrations of L-phenylalanine are harmful to human brains 
in at least three situations: 

(a) In older than 6 months old children and adults with mature brains,
high blood concentrations will prolong performance time, slow brain
wave cycles (EEG) and reduce neurotransmitter  production in a
reversible manner.

(b) In newborns to 6 months old with rapidly growing brains elevated blood 
phenylalanine produces irreversible brain damage by slowing migration of 
oligodendroglia (brain cells) and altering myelin  (nerve insulation) 

(c)    In pregnancy, if the mother's blood phenylalanine is raised in high 
concentrations, her child's brain development can be irreversibly damaged. "

( )

* * * * * * * * * *

INTERRACTIONS:  (the following are drugs that I have identified that
interact with Phenylalanine)
Antidepressant Medications, Monoamine Oxidase Inhibitors (MAOIs) -
Phenylalanine may cause a severe increase in blood pressure in people
taking MAOIs (such as phenelzine, tranylcypromine, pargyline, and
selegiline). This severe increase in blood pressure (also called
"hypertensive crisis") can lead to a heart attack or stroke. For this
reason, individuals taking MAOIs should avoid foods and supplements
containing phenylalanine.

Baclofen - The absorption of baclofen, a medication used to relieve
muscle spasms, may be reduced by phenylalanine. Therefore, it is best
to avoid taking this medication with a meal, especially one that is
high in protein content, or with phenylalanine supplements.

Levodopa - A few case reports suggest that phenylalanine may reduce
the effectiveness of levodopa, a medication used to treat Parkinson's
disease. Some researchers speculate that phenylalanine may interfere
with the absorption of this medication. Therefore, phenylalanine
should not be taken at the same time as levodopa.

= = = = = = = = = = =

The following are articles I have found regarding the safety of an
individual who takes phenylalanine:

?The U.S. Food and Drug Administration has placed phenylalanine on its
GRAS (generally recognized as safe) list, largely due to it vast usage
and because of the availability of scientific literature showing the
safety and non-toxic nature of PA.

Additional less documented and as yet unsubstantiated uses have been
for improving memory, increasing mental alertness, promoting "sexual
interest", and the suppression of appetite. Considering the various
effects produced during depression, and the ability of phenylalanine
as an anti-depressant, these uses may be more of a consequence of the
depressive state that has been modified.?

Source:  Nutrition Farm
( )

* * * * * * * * * * *

The Food and Drug Administration classifies phenylalanine as ASP,
meaning ?Fully up-to-date toxicology information has been sought.?

Source:  Food and Drug Administration GRAS List
( )

* * * * * * * * * * *

?It may not have been proven, however, that taking phenylalanine
supplements of, let's say, 500 mg a day will straighten out the
absence of sexual desire. The dosage may be insignificant, or there
may be limitations to absorbency, and so on. Conventional wisdom is
that taking phenylalanine supplements will not hurt one's sex and
general life (unless one is a phenylketonuric), while it may or may
not mean an improvement.

For its prosexual benefits, phenylalanine is certainly not a wonder
drug such as Viagra.

Among the additional alleged health benefits of phenylalanine and
phenylalanine supplementation are a use in the suppression of pain and
as an weight loss aid through the suppression of appetite.?

* * * * * * * * * * *

?To people who are not phenylketonurics, there is by and large little
danger from phenylalanine, especially if it's part of a normal diet.
The exception are people on monoamine oxidase inhibiting drugs (MAO
inhibitors), as phenylalanine is converted into the amino acid
tyrosine. If the enzyme which breaks down monoamines such as tyrosine
is inhibited, the body is flooded with substances that can cause
extreme hypertension. ?

( )

If this answer requires further explanation, please request
clarification before rating it, and I'll be happy to look into this

Google Answers Researcher

Additional Sources:

Food & Drug Administration
( )

Web MD
( )

National Research Council:
( )

Google Search Terms:

phenylalanine safety reports
( :// )

libido phenylalanine reports
 ( :// )

Clarification of Answer by nenna-ga on 11 Jul 2005 12:55 PDT
I would like to clarify that 1 Gram (gm) = 1000 Milligrams (mg)

If you are taking 5gm a day, that is equivalent to 5000 mg a day. 
Please note in my answer above, DOSES IN EXCESS OF 5,000 MG A DAY MAY

johnman-ga rated this answer:5 out of 5 stars

Subject: Re: Hi
From: crabcakes-ga on 11 Jul 2005 13:19 PDT
I'm curious as to *WHY* you are taking phenylalanine. It has been
shown to be slightly helpful in depression and in treating vitiligo,
but it can exacerbate dyskinesia in sschzophrenic patients.
Subject: Re: Hi
From: johnman-ga on 11 Jul 2005 13:37 PDT
Thanks for that thorough well-researched answer.
The reason I am using phenylalanine to improve libido is as follows:
L-Phenylalanine freely crosses the blood-brain barrier ( unlike
Tyrosine) and is converted into Norepinephrine, the neurotransmitter
thought to be responsible for libido. The antidepressant, Wellbutrin,
works in similar fashion. But you need mega doses of phenylalanine ie,
about 5gm/day to achieve this effect. It also helps if you maintain a
state of relative hypoglycemia throughout the day.
Subject: Re: Hi
From: crabcakes-ga on 11 Jul 2005 14:58 PDT
Hi johnman, 

  It was Nenna-ga who gave you your answer! I'm another researcher who
found your question interesting!

   Regards, Crabcakes
Subject: Re: Hi
From: johnman-ga on 11 Jul 2005 15:22 PDT
I WAS thanking Nenna-ga( since he was the one who researched the answer.
Subject: Re: Hi
From: nenna-ga on 11 Jul 2005 16:46 PDT
Thank you very much for the rating and I am glad that I was able to
help you.  If you need anything further, please let me know!

Subject: Re: Hi
From: nenna-ga on 11 Jul 2005 16:49 PDT
PS - for the records, I'm a she, not a he :)
Subject: Re: Hi
From: johnman-ga on 11 Jul 2005 18:15 PDT
Sorry about the gender mixup...alas my MCP traits have been exposed!

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