Hello - thanks for asking your question. Please keep in mind that I
am an internal medicine physician and not a psychiatrist, although I
consulted a few of my psychiatry colleagues for this question.
You asked the following question:
"Please provide the exact differences between name brand Prozac verus
generic and an explanation for the differences patients may experience
As you have mentioned, there have been anecdotal reports of generic
fluoxetine not being as efficacious as Prozac. There are many types
of generic forms available, and I cannot give an exact ingredient
comparison because they are not available:
"To date, more than 20 companies have received approval or tentative
approval for almost 50 generic fluoxetine products. The approval
package data (which includes bioequivalency data) for these agents are
not yet available."
There have not been any clinical trials comparing the efficacy of
generic fluoxetine and Prozac. From Current Psychiatry:
"Some anecdotal reports have suggested a clinical difference, but
these claims have not yet been supported in the literature . . .
Still, there is no evidence that generic fluoxetine is less effective
than Prozac, despite increased attention from patients, clinicians,
and pharmaceutical companies."
As for the differences between the generic and Prozac, the FDA
requires that they contain the same active ingredient. The generic
must show in a study that the amount of active ingredient be between
80-125% of the brand name product. As there are almost 50 different
generic products, the fillers will most certainly vary:
"The FDA requires that generic products contain the same active
ingredients as the brand name product; however, the inactive
ingredients used in the formulation, for example a pill or capsule,
may be different. These inactive ingredients are sometimes called
fillers and may or may not affect how the medication works in your
For approval of its generic product, the generic manufacturer must
show in a bioequivalency study that the amount of active ingredient
delivered from the generic product to the test subjects' bloodstreams
is, on average, 80 - 125% of the amount delivered from the brand name
drug. Meeting this standard allows the FDA to approve the generic
product as a "therapeutic equivalent" that is considered "safe and
However, just as individuals vary, individual responses to the same
medication may vary as well. Although a therapeutically equivalent
generic drug product is considered safe and effective, an individual
may respond to a generic equivalent differently than he/she responds
to the brand name product."
Again, after a Medline search, there have been no clinical trials
comparing generic fluoxetine and Prozac.
As for explainations for the differences, the article from Current
Psychiatry suggests that the symptoms of depression wax and wane, a
reverse-placebo effect, and since the bioavailability only has to be
within the 80-125% range, there is a possibility that the generic may
contain less active ingredient than Prozac:
"Some clinicians have found that select patients require a higher
dosage of generic fluoxetine than Prozac to control their symptoms,
but several issues may contribute to these increased requirements.
First, depression and depressive symptoms wax and wane; an increase in
symptoms may be part of the course of illness rather than differences
between brand and generic formulations.
Increased symptoms may also reflect patient bias. The patient knows he
or she is taking a generic and may be more inclined to notice or
report symptoms. Additionally, some patients who believe generics are
less effective than brand-name equivalents experience a reverse
placebo effecttheir belief that a generic drug is inferior diminishes
its effectiveness. Finally, subtle differences in bioavailability and
bioequivalence between the brand-name and generic drugs may be seen
Regarding your last question:
"If you are able to find these answers, then please also offer an
explanation as to why after 1 year on name brand Prozac and a 30 days
trial of generic that fails in effect, a patient might no longer
experience a benefit from the name brand either."
I called and discussed this issue with several psychiatrists in my
area. They could not come up with a concrete answer, but came up with
a few hypotheses. One had suggested that it may be simply due to the
waxing and waning character of depression. Another suggested that if
the generic was truly "subtherapeutic" (i.e. contained less active
ingredient than Prozac), then they may have "relapsed" into depression
and would then require a higher dose to control their symptoms.
Again, I am not a psychiatrist and there have been no clinical studies
for this question.
I stress that this answer is not intended as and does not substitute
for medical advice - please see your personal physician for further
evaluation of your individual case.
Please use any answer clarification before rating this answer. I will
be happy to explain or expand on any issue you may have.
generic prozac differences
prozac vs generic fluoxetine