Positives

• Casein protein comes up around nutrition and sleep in ME/CFS patient conversations, with one patient using very small servings of a casein-containing product and reporting better neurocognitive symptoms and sleep. Reddit.

Negatives

• Casein and casein hydrolysate potentiated intestinal histamine release six- and four-fold respectively in lab work, while whey hydrolysate did not, making casein particularly problematic for histamine-sensitive patients PubMed.
• Patients with Long COVID often develop new or worse food reactions, with milk proteins (whey and casein) becoming triggers when the immune system is in high alert Long COVID Justice.
• Casein allergic reactions trigger histamine release that can cause hives, rash, and red itchy skin in sensitive patients WebMD.

Hurdles & Side Effects

• The same story also involved dose reduction and caution after problems, so patients sensitive to dairy, casein, or gut symptoms may need to treat it as a nutrition tolerance experiment rather than a simple protein upgrade. Reddit.