I used it once and it gave me a number of small ulcers in my mouth/back of my throat after about 2 weeks. Hurt like hell for almost a week. I read that if you're prone to cold sore, arginine products can have this effect but I've used other since and never had that problem again. Also, Xpand was the only one I used daily, other NO-type drinks I've only used sporadically for energy.