How long does pot stay in your system?

How long does pot (or other drugs) stay in your body? Is there any way to detect it?

Pot stays in your body, stored in fat tissues, potentially your whole life. However, it is very unusual to be released in sufficient quantities to have an intoxicating effect or be measurable in urine screens. Heavy pot smokers, people who have smoked for years on a daily basis, very commonly have detectable amounts in their urine for at least two weeks. In these cases, pot may periodically reappear following heavy physical exertion or weight loss as it is released from fat stores.

Other hallucinogens, such as LSD, are also thought to be stored in fat. Some believe this may cause a "flashback phenomenon," the re-experiencing of LSD highs actually caused by release from fat. LSD is not detectable in urine. Other commonly abused substances are typically out of your body as you pass them out of the urine. In experience, most opiates and cocaine are free within 36 hours. Benzodiazepines (or drugs given for anxiety) may persist for up to several weeks but are usually out in three or four days. Amphetamines (such as crystal meth) are typically undetectable at 36 hours.