I am so grateful for this site. I can ask questions that would make the people in my life seriously concerned about me!
Can someone on meth or cocaine operate a car and abduct someone without getting pulled over? How much rational thought does the drug take away from tasks that involve planning and judgment? Would the character need to be on the end of a high?
Where I grew up, it was common knowledge that long-haul truck drivers would dissolve methamphetamine in soft drinks, and sip it over the course of their drive (less intense high but longer duration compared to snorting, smoking or injecting). It was the only way to meet schedules which often required someone to drive a truck for 60 hours continuously without sleep.
In general, methamphatamine makes someone fixate on one activity and do it for a long time (we're talking 8-12 hours). Examples I've seen include dancing the exact same steps over and over all night, cleaning the house, collecting shellfish (which you then might not even eat because the drug suppresses appetite), having sex that doesn't lead to climax, walking or driving along the same street / block looking for a specific person / group of people (ex-girlfriend or rival gang members), talking about the same thing over and over. It is popular among jobs such as computer programmers and film editors, since their work involves long hours of repetitive tasks.
It is plausible that it could make someone want to carry out a kidnapping. It makes people violent and paranoid. They often believe that friends are secretly plotting against them, or that the police / rival gang members are about to raid their house. Occasionally this even gets to the point where they stab random strangers in the street. This paranoid behaviour tends to increase the longer the user has gone without sleep (the drug has a long duration of action, and often users will take another dose before the first one has worn off, doing this for up to a week and then sleeping for 24-48 hours solid).
Regarding planning things, someone on methamphetamine can invest huge amounts of time and effort into planning something. But at the same time they often completely forget about critical details (like Homer Simpson's "D'Oh" moments). A real life example was two people from my high school, who were arrested for murdering their dealer. They hadn't thought about what to do with the body or the murder weapon, even though they had planned out the whole thing in advance.
Can't talk about cocaine in the same detail, but I know not only costs more per dose than methamphetamine, but each dose wears off much more quickly (under an hour vs. many hours). Users that are high on it don't have the same level of focus as methamphetamine users. They could still drive a car though.
