I thought Zyrtec might b/c I saw drowsiness listed among its “side effects”. I regularly use melatonin & CBD, and occasionally theanine, but I haven’t tried l-arginine. I use an extremely small amount of melatonin sublingually, and while it does get me to sleep it also promotes exhausting dreams. I’m trying various things/combinations (including exercise) to enable me to sleep soundly, with minimal waking up and without long, tiring dreams. Aka the holy grail LOL.
I max out with 10 mg melatonin. That it is a potent antioxidant is a welcome side effect.
L-arginine is not ordinarily considered a substance that has much to do with somnolence. But I and others, initially taking it for something else have noted the effect.