Hello I believe I can help you with your concern
Yes you are very much correct that as we age, especially past 60 years of age, we metabolize most medications, including antidepressants and antipsychotic medication at a slower rate, which leaves more medication being present in the body
Now it really depends on what antidepressants are being used and what antipsychotic medications are being used, but sometimes the combination of these two can lead to something called Serotonin Syndrome, which can be fatal. Now usually a low dose antipsychotic combined with a SSRI antidepressant will not cause this Serotonin Syndrome, but if your friend is metabolizing these medications at a slower rate, then that could mean more Serotonin being present in her system allowing for a possible chance of Serotonin Syndrome. This is just one example.
Also most antipsychotics at higher dosages can cause more adverse effects with the elderly and this can also be possible at standard dosages with someone with someone who is elderly as well due to the slow metabolizing factor.
This is why most elderly (individuals above 60 years of age) are carefully monitored by a psychiatrist and usually given lower doses than the standard dose.
Sometimes psychiatrists will go at a higher dosage if the benefits outweigh the risks
For example, studies show that a popular antipsychotic called risperdal can be increased gradually to around 1 to 1.5 mg for maximum effectiveness in the elderly. Higher dosages than this are not shown to be more effective and can increase the risk of side effects. In addition, there should be blood labs to monitor the glucose and prolactin while on risperdal. Also Risperdal can also increase the risk of stroke.
So I would agree with your concern and recommend that your friend at least get an evaluation from a geriatric psychiatrist, as these specialize in mental health treatment for individuals above 60 years of age, to help your friend get the most optimal dosage of the medications she is one with a minimal risk of side effects.
In addition, many antidepressants and antipsychotic medications may accumulate in the body and as the body metabolizes the medication at a slower pace this means more medication is accumulated in the body over time and this can increase the risk of adverse effects, which is another reason why lowering the dosage may be necessary and another reason why being reevaluated by a geriatric psychiatrist is a wise decision for your friend.
I see that you are offline or away from your computer right now, but when you get back online I would be very interested in continuing this discussion with you and talking about anything further you would like to share regarding your concern, so if you respond in the chat box I will be able to get back to you as soon as possible.