I've seen heavy use described as more than once a week especially in these latest "studies" about pot and schizophrenia. Keep in mind that a lot of these studies are theoretical. It wouldn't be ethical to force teenagers to smoke to conduct research so a lot of these so-called findings are calculated, not actually observed. It's also worth mentioning that in the US there is no clean, controlled source of research MJ outside of that grown under the watchful eye of the DEA at the University of Mississippi.