[Pseudoscience-is-malarkey (OP)]

Is it possible for the psychoactive components of a drug to take effect on the human brain within seconds like we too often see in the movies?

[alancalverd]

Yes. Consider normal anesthetic procedure: "Please count down from ten" - very few patients get below five before joining the fairies.

[Bored chemist]

Nicotine reaches the brain within about 10 seconds of smoking.

[CliffordK]

It is all about delivery method. So, inhaled will get in much quicker than oral.  What about IV dosing?

I'm not sure I've ever had any, but I presume "Laughing Gas" has rapid onset.

[Pseudoscience-is-malarkey (OP)]

There was a case in Canada where an unstable woman named Cindy James, who obsessively alleged that she was being watched and harassed, wound up dead with her legs and arms bound together and a high dose of heroin in her system. The Canadian police declared it an obvious murder case, as someone with that amount of dope in their system could not tie themselves in such a way. Eventually, it was a journalist (not a physician) that pointed out that even if the drug was administered intravenously, it should have taken 10-15 minutes to reach her CNS. He then hired a woman matching the dead woman's age and physical characteristics to see if she could tie herself up the same way within 10 minutes. She was able to.

[vhfpmr]

I presume "Laughing Gas" has rapid onset.

IME it takes quite a few breaths before you get a big enough dose, so I think it might be difficult to define the time precisely.

[Pseudoscience-is-malarkey (OP)]

And

[inquisitivemind]

Speaking from experience working in a psychiatric facility, yes, there are drugs that start working within seconds, but they are typically the sedative ones, and are either given IM (i.e., Haldol) or a dissolvable (i.e., Zyprexa Zydis).  Other psychiatric or psychoactive drugs, such as mood stabilizers or anti-depressants typically take several days, if not weeks to start working, at least to the full extent they can.

[Origin]

After one inhalation of pot the effects can be felt within a few seconds, so the answer is yes.  If a drug is taken orally the effects can take between 20 minutes to over an hour, so the answer is no.  IOW it depends on the drug and the method of delivery.

[Bored chemist]

Speaking from experience working in a psychiatric facility, yes, there are drugs that start working within seconds, but they are typically the sedative ones, and are either given IM (i.e., Haldol) or a dissolvable (i.e., Zyprexa Zydis).  Other psychiatric or psychoactive drugs, such as mood stabilizers or anti-depressants typically take several days, if not weeks to start working, at least to the full extent they can.

This is actually a more interesting point.
It's easy to see how a drug in the blood affects the brain within seconds- because that's how long it takes the blood to get from your arm or lungs or whatever to the brain.

It's much more interesting that some drugs take weeks to work.