It has been widely claimed that the dosage levels of psychoactive drugs from second-hand marijuana smoke is insufficient to have an effect - i.e. to give a "contact high"
The notion of the “contact high” is a myth. In order to get “high”, the amount of active THC in your bloodstream has to spike.
Many users, and friends of users of marijuana report experiencing a “contact high.” That is, they purport to experience some of the effects of marijuana simply by being in contact with or around those using marijuana. Virtually all users wrongly attribute this experience to the inhalation of second hand smoke. This is unlikely for a number of reasons. Since exhaled smoke is virtually devoid of psychoactive substances and is widely dispersed in the surrounding air, it is not possible for one to inhale even a small fraction of a working dose. Additionally, many, including noted pharmacologist and psychedelic researcher Alexander Shulgin, report similar experiences involving drugs that are not inhaled, indicating that these effects are due to different biological processes.
However, this doesn't tally with the anecdotes and claims of others:
I'm allergic to marijuana, so I've gotten coughing and asthma from second-hand smoke, and also I get painful sores on my head when the neighbor smokes it. It gives me mood swings, then I smell her pot half an hour later. One time I was very, very tired from the marijuana smoke coming in, then when it wore off, my heart beat really fast for a couple of hours
Exposure to second hand smoke can cause a drug test to be positive. A "contact high" indicates that THC has entered the blood stream where it is then detectable by drug analysis.
However, despite there being evidence that the second hand marijuana smoke can produce a very small high in people, there is no evidence that the smoke can cause a failed drug test.
My personal experience is that even walking a few meters behind a person smoking a joint outdoors is sufficient to give me symptoms 20 minutes later, such as a strange feeling in the head area, slight alteration of taste, vivid dreams, slight insomnia, and an infuriating loss of higher mathematical ability.
What does the evidence say? Can the miniscule dosages inhaled this way lead to real signs of a small marijuana high, or are these symptoms of a nocebo effect?