Hi there.
Effexor or Venlafaxine is an effective drug to control menopausal symptoms such as the hot flashes and mood swings. Though you are correct that this can have side effects similar to what she's experiencing now, these side effects are not that common and I believe the benefit that she can derive from this drug far outweighs the potential risk of side effects.
Also, I believe that putting her on Effexor is only a temporary measure so as just to control the present symptoms. Once the body get used to the effects of tamoxifen and the symptoms controlled, the effexor can be gradually discontinued.
Regards to you and your friend.
I generally don't disagree with doctors on here, especially Dr Paul, but effexor has rather substantial side effects and is extremely difficult to wean off of. I would do some serious research before deciding that the side effects are worth whatever benefits in terms of relieving menopausal symptoms. There are far less dangerous alternatives for controlling menopausal symptoms. Just my opinion. Also, the side effects are more common than the drug company reports, according to the research I have done. Get a second opinion on the effexor and do the research before making up your mind.