http://www.abreastinthewest.ca/medical2.cfm?Num=43
Play the Odds: Supplements and Chemo  Summer 2003 Vol.4 No.
Robin O’Brien BSc, BScPharm, PharmD, BCOP
Drug Information Specialist, BC Cancer Agency

Last December, a woman called to say thank you for suggesting she avoid
using supplements during her chemo. News that taking supplements could
counteract the benefit of breast cancer treatments was all over the front
page of the Vancouver Sun that morning. A few months before, she was
shopping for opinions after being urged to take a tote bag full of various
supplement pills along with her chemo. Now, she was finished treatment.
Supplement free.

I had to ask myself what made me so cautious about combining supplements
with chemo before there was a study to say one way or the other. What did
I know about chemo that gave me so much respect for the power of herbs and
supplements?

Chemo is like walking a tightrope. It’s a fine balance where too high a
dose is too toxic and too low a dose doesn’t work properly, so cancer
cells can escape. As well, while some cancers are exquisitely sensitive to
the effects of chemo and some are completely resistant, most are probably
in between and could be pushed in one direction or the other. Who knows
what herbs and supplements could do to this balance.

Most herbs haven’t even been tested with the notable exception of St.
John’s Wort. This popular herb is clinically proven to be helpful, and as
good as some prescription drugs, for mild to moderate depression, a common
problem for cancer patients. A cancer care team in Europe noticed that
people taking St. John’s Wort had fewer side effects than usual while
having chemo with a drug called irinotecan. No wonder - there was a drug
interaction. Chemo blood levels had dropped by half and it didn’t work
properly anymore. But that’s not all that St. John’s Wort can do.

St. John’s Wort can cause cells to sprout little drug pumps called PGP.
This is a worry because PGP can cause multi-drug resistance to chemo. As
fast as the chemo is transported into the cancer cell, PGP pumps it out
again. This is all part of the body’s natural protection against poisons,
which is especially important for plant-eating creatures like us. But the
net result can be resistance to chemo.

There is a lot of uncertainty about what happens when herbs and
supplements are combined with chemo. This makes the decision difficult.
Some women prefer to avoid herbs and supplements because they feel that
they have too much to lose or, if they are going to have chemo, they want
to be sure that they are getting the full benefit. Others, like those
who’ve already had a recurrence, may feel that they have little to lose.
<read the rest of that article there and other more recent articles there>