The data for PQQ’s safety is excellent, at least for limited or short-term use (e.g. up to a year) in humans and longer-term use in animals. Long-term (multiple year) safety in humans remains to be assessed. However, based on pyrroloquinoline quinone direct to market sales, it may be concluded that hundreds of individuals now take PQQ. Some of these users tend to be aggressive about supplementation (including myself), so the chance that an interaction with PQQ may be adverse seems highly unlikely based on the lack of any published reports.
Although there are no direct studies on the potential interaction of PQQ with psychotropic drugs, several studies suggest that the idea is worth exploring. What data that are available regarding cognition are in two animal studies and one human study (see below). The human study is well controlled and the results of the study suggest that PQQ alone or with CoQ10 may be useful for improving higher brain function. Likewise, the animal studies are supportive of this perspective.
To be very clear, not all these supplements and medicines work independently? The best answer about food supplementation and drug interaction is going to come from your personal physician and pharmacist. Although one can identify major mechanisms or even specific functions for given compounds, from a global physiological perspective, there can be cross talk between the numerous cell-signaling pathways that control cellular function and an enzyme cofactor may interact with numerous enzymes each with a specific function.
2: Ohwada K, Takeda H, Yamazaki M, Isogai H, Nakano M, Shimomura M, Fukui K, Urano S. Pyrroloquinoline Quinone (PQQ) Prevents Cognitive Deficit Caused by Oxidative Stress in Rats. J Clin Biochem Nutr. 2008; 42:29-34.