What substitutes work with a capsaicin allergy?
You could try other piperine containing types of peppers (Piper genus), these include P. longum (long pepper) and P. retrofractum, as well as white pepper P. nigrum, though any member of the Piper genus should contain some piperine, but amounts and hence spiciness will vary.

You could also try ginger (Zingiber genus), as well as mustard seeds and shoots/leaves (Sinapsis genus and Brassica juncea), all of which are objectively "hot", though also with different (and strong) flavours and heat levels.

Wikipedia also has a list of peppers under their Template:Herbs and Spices, which includes such things as Alligator pepper (Aframomum), Schinus genus, Sichuan pepper (Zanthoxylum), and a couple of others.