Note. For context, I wrote this article primarily in the context of the suitability of patients with bipolar disorder, although some parts of the article are more universal.
Quetiapine
It is an antagonist of dopamine and serotonin receptors (antagonist means that it reduces the effects). The combination of quetiapine with SSRIs is inappropriate because quetiapine weakens all the positive effects of SSRIs (antidepressant and anti-anxiety effects). SSRIs, on the other hand, work on the principle of increasing the activity of all types of serotonin receptors.
Quetiapine also acts as an antagonist at muscarinic acetylcholine receptors. This has its advantages and disadvantages. It reduces the negative side effects of reduced dopamine receptor activity, such as muscle tremors and motor problems, e.g. stiff legs (which are also symptoms of Parkinson's disease).
The disadvantage of antagonism at muscarinic acetylcholine receptors is the slowing of the metabolic process and the slowing of digestion, which has the potential to lead to weight gain.
(Parkinson's patients who suffer from low activity of dopamine receptors also use antagonists for muscarinic acetylcholine receptors).
The side effects of quetiapine can be eliminated by drugs with opposite effects from the parasympathomimetic category.
Some antipsychotics, on the other hand, act as agonists on muscarinic receptors.
Aripiprazole
It has interesting effects in that it increases the effects of some types of serotonin and dopamine receptors and decreases the effects of others (It acts on some subtypes of these receptors as both an agonist and an antagonist).
Combination with SSRIs is inappropriate because it can increase the efficacy of the serotonin receptor subtypes on which aripiprazole acts as an agonist by up to 100-fold.
There were also significant differences in the side effects that types of SSRIs caused, and which caused less havoc with drug interactions with SSRIs.
Aripiprazole can and should be combined with buspirone, which is an anti-anxiety drug based on a different principle than SSRIs.
The combination of aripiprazole and SSRI may cause hallucinations.
Sulpiride
The positive aspect of this antipsychotic is that it can be combined well with SSRIs, as it does not act on serotonin receptors but exclusively on dopamine receptors. A psychiatrist is allowed to prescribe such a drug even to a bipolar patient.The real sense for a bipolar patient to take this medicine is only during manic episodes, when the activity of dopamine receptors is higher.