The bioavailability problem is the whole story on this page.
Unformulated curcumin is poorly absorbed: 2 g taken alone left serum levels undetectable or very low in healthy volunteers (PMID: 9619120), and on a dose-normalized basis 1,800 mg of unformulated standard curcumin was absorbed 45.9-fold less well than a 376 mg dose of a hydrophilic carrier formulation (PMID: 24461029).
The formulation classes with human absorption or human outcome data in the trials below are piperine co-administration, phospholipid phytosome, turmeric volatile oil, hydrophilic carrier, and the Theracurmin form used in the memory trial.
Each has different pharmacokinetics, and delivery system matters more than the milligram count on the label.
On interactions: piperine, the co-factor in many curcumin products, is described as an inhibitor of hepatic and intestinal glucuronidation (PMID: 9619120).
That is the mechanism by which it raises curcumin exposure, and it is a reason to review any curcumin plus piperine product against current medications with a clinician.