It is very addictive, the more you take it the more you need it. Eventually the brain gets to where it can't feel "normal" without it, but like any drug some people are more susceptible than others. Some people can do it once and walk away, others take it once and are seriously hooked.

My son's father did it, but he wasn't always high. When he was off it, he was normal. When he was at the high, he was excessively everything, (it very closely resembles extreme mania) when he was coming down is when he was hardest.