Pepper increases absorption of turmeric.

Piperine, a compound found in black pepper that's responsible for its pungency, can greatly improve absorption of turmeric in the body.

https://www.jenniemiremadi.com/blog/the-top-4-ways-to-get-the-most-out-of-turmeric

"curcumin...cannot be utilised because of poor bioavailability due to its rapid metabolism in the liver and intestinal wall...piperine, a known inhibitor of hepatic and intestinal glucuronidation... Concomitant administration of piperine 20 mg produced much higher concentrations from 0.25 to 1 h post drug (P < 0.01 at 0.25 and 0.5 h; P < 0.001 at 1 h), the increase in bioavailability was 2000%"

https://www.ncbi.nlm.nih.gov/m/pubmed/9619120/