@spiritguided1, I think I would discuss the supplement with my doctor before trying it. I did a search and didn't see anyone on Connect mention it's use to help with PMR and I saw this warning on WebMD. Although it doesn't specifically mention PMR it does mention other autoimmune conditions and could make the symptoms worse, just my non medical opinion though which is why I would check with my doctor first.

"Auto-immune diseases such as multiple sclerosis (MS), lupus (systemic lupus erythematosus, SLE), rheumatoid arthritis (RA), pemphigus vulgaris (a skin condition), and others: Lion's mane mushroom might cause the immune system to become more active, and this could increase the symptoms of auto-immune diseases. If you have one of these conditions, it's best to avoid using lion's mane mushroom."
-- Lion's Mane Mushroom - Uses, Side Effects, and More:
https://www.webmd.com/vitamins/ai/ingredientmono-1536/lions-mane-mushroom
Do you mind sharing which medications you have tried that have failed to help your PMR?