@pierwell The website drugs dot com has a lot of useful information. You need to do your own internet search to find the specific webpage since it appears posts with active hyperlinks are rejected.

Of particular interest is

consumption of higher dosages (up to 240 mg of lithium orotate per day), with no apparent signs of toxicity

However I believe a 5mg dossage may be too low. Yes, extrapolation from the dosage given to the mice suggests that a dose of anywhere between 1 to 10 mg may be effective. Do an internet search on raffaelemedical and lithium-orotate-and-alzheimer-s-harvard-study-reveals-a-breakthrough-in-brain-aging. Not that it matters much, but my own extrapolation reached the same conclusion – actually as little as 2 mg may be effective).
HOWEVER, you need to keep in mind that the mice were fed the Lo in their water and they were actually young rats which developed the condition because they were totally deprived of lithium.
This is important as it relates to how the humans developed the disease at an OLDER age. A rational supposition is that it was due to age related degradation of the digestive system leading to a reduced absorption of Li from food. Thus, the dosage in pill form needed to deliver the same amount of Li to the human brain may be MUCH higher.
You may consider say a 20mg dose – especially since that is the highest dosage in one pill I could find on Amazon. You could look at the reviews to see if you find anything that might be important in your case in question.