The Drug Awareness Warning Network Annual Report, published by the US federal government contains a statistical compilation of all drug deaths which occur in the United States. According to this report, there has never been a death recorded from the use of marijuana by natural causes. Unlike opiates, barbiturates or amphetamines, there seems to be little risk from the use of large amounts of marijuana. When a person smokes too much they feel very tired and lie down. When people swallow large amounts of hashish, occasionally they get sick to their stomach.

Marijuana's effect on the user depends on the strength or potency of the THC it contains. THC potency has increased since the 1970s but has been about the same since the mid-1980s. The strength of the drug is measured by the average amount of THC in test samples confiscated by law enforcement agencies. THC is the chemical in marijuana which makes you feel "high" (which means experiencing a change in mood and seeing or feeling things differently). Certain parts of the plant contain higher levels of THC. The flowers or buds have more THC than the stems or leaves.