I had been taking this supplement for a little over a month. I had a metabolic panel done and my b12 was extremely low. I was experiencing extreme fatigue and nerve pains. I discussed it with my PC and she recommended an OTC supplement. This supplement definitely gave me energy and relieved my nerve pain very quickly; however, it also gave me an assortment of other side effects: Nerve spasms (painless, but persistent and concerning) Extreme itching over my abdomen and legs Abdominal cramps similar to a UTI Constipation Anxiety and panic attacks Insomnia Heartburn My hands swelled up while taking a routine walk with my dogs and my legs got a similar flush to taking niacin except the burn was UNBELIEVABLE. I stopped taking this supplement and within three days the crazy subsided. B vitamins are water soluble so they are supposed to flush from your body pretty quickly and there is not an established upper intake limit. But the comments not accepted RDA is 2.4 for adults. This is twice the RDA. Also methylated forms of B vitamins are the active, more absorbable form. This was way way way too much for me. Maybe I'm allergic, I don't know that I will try taking b12 in another form or dosage. Just pay attention to your body and talk to your doctor