Is it a logical side effect of the medication that he was unable to hold his bowels, and had to train himself to do this again?
Or is Lucas blaming his medication for something that was actually physiologically or mentally his fault?
I guess what I'm saying is, is it common that the antipsychotics would make someone shit and piss themselves, or is that just Lucas?
Yes it is possible some anti schizophrenia drugs
may lead to incontinence and loss of sensation regarding bowels and urination. These types of drugs act on the alpha receptors and they can lead to decreased nerve sensation, most likely Lucas was experiencing reduced nerve sensation in his GI tract and urinary tract, if the medications were to blame.
Here is an
article about antipsychotic drugs
However, i have another theory, Lucas may have also lost control of his bowels due to stress from being in the psych ward, and giving that he is taken out of his usual environment, he became panicked and devoted sensory attention to other parts of his brain most likely neglecting the autonomic nervous system (hunger, thirst, digestion, bowel control). It could also be that since Lucas is hyper-fixated on his illogical quest to get women, that when he was taken away from other stimuli, this was all he thought about and neglected, as he usually does, all other bodily functions.
I also believe that Lucas is a characteristic dull IQ (70-89) individual and he might have bowel problems on a regular basis without taking drugs and medications. Notice how he often pauses and elevates his tone unnecessarily, Lucas is also a one track mind guy, he often does not think about normal daily routines or put effort into cleaning, bathing, and other hygiene behaviors, these are common characteristics of dull and low IQ individuals. I also noticed in an earlier video he said he was taking omeprazole, which is an acid reflux controlling drug, so he might have also had IBS (acid reflux and IBS commonly are comorbidity) IBS often can lead to loss of control of bowels due to poor bowel anticipation.
But to answer your question, i think that Lucas could have suffered incontinence from the antipsychotics. But there are also many other plausible answers.