Non-spicy flavors for a spicy-hot food lover?
It depends on the medical reason. If it's a sensitive esophagus or stomach caused by GERD, replacing the capsaicin with pungent components, like mustard or black pepper, or strong acidic or base components, like vinegar, wine or citrus, may be out as well. Even alumvarics like onions and garlic may be out. By contrast, ginger can provide intense heat on the tongue, but is also recognized as a remedy for stomach upset. They will need to check with the doctor or nutritionist to see what's OK.

Used well, the boring old residents of the spice rack can provide strong and piquant flavor profiles without the irritation hot peppers in all their incarnations can introduce. Many traditional Continental, African, Near Eastern (Including Greek) and East Asian recipes that don't rely on heat for flavor are "adapted" for a mid-20th century Anglo-American palate - they're blander and less complex than the originals. Seek out traditional recipes and techniques, or 21st century interpretations, rather than rely on outdated Anglicized recipes. Don't be afraid to explore uncommon cuisines as well - Afghan cuisine, for instance, is very mild yet intensely flavorful - a mix of Near Eastern and Indian flavors that doesn't rely on heat.

Here is an article on intensifying and improving the flavors of commonly used spices and herbs. In summation:


Use fresh and freshly ground whole spices (I use a "magic bullet" style blender) rather than stale pre-powdered preparations.
Use fresh, green herbs rather than dried flakes - oregano is the exception.
Toast whole spices in a pan on low heat before they're ground, or bloom herbs and spices in hot oil, and use the oil as the flavorant.


Here is an article on common techniques to build strong flavor in dishes without introducing spiciness. In a nutshell -


Bloom the spices (as above)
Roast vegetables rather than sauteé, steam or stew.
Don't neglect the aromatics, such as sofrito or mirepoix. (Here is another article on selecting and using aromatic components)
Confit (poach in oil) powerful aromatics like garlic.
Use hygroscopic seasonings (salt or sugar especially) to draw out water and intensify flavors.
Brown butter before introducing it to the recipe.