me - 100mg to 120mg of Prozac (fluoxetine) is a very high dose. I do not understand the rationale behind taking a daily dose of this size. Usually doses beyond 60mg daily are not necessary, as at this level (in most people) the serotonin reuptake receptors are fully blocked and giving any more of the drug will have no therapeutic effect.

In other words, the dose response curve flattens because there is nothing more that extra Prozac can do. The doctor may have some rationale for giving a dose this high: your sister may not absorb Prozac very well and she needs doses this high just to obtain sufficient concentrations at the receptors, similar to the concentrations achieved other people at much lower doses. The rest of her Prozac dose is not absorbed and travels straight through her intestines and is excreted unchanged in her feces.

Your sister should not lower the dose on her own. She must be weaned slowly from doses this high to avoid withdrawl syndrome. She should perhaps ask her doctor (a psychiatrist, I am hoping) why she is taking double the normally highest dose. Her pharmacist should also have asked the doctor why her Prozac dose is so high; he/she may know the reason. Lastly, your sister could consult another psychiatrist, just to be certain that this dose is warranted.

There really is not much to worry about at doses this high, except that some side effects (ie. due to secondary receptor binding effects) may be much more pronounced. The specific side effects that she would experience (if any) would be related to the rationale behind the reason for giving a daily dose this high.

In any case, your sister should talk to her doctor as to why her dose is this high. I hope that this helps. - Cam