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FellowConspirator t1_j6dkil3 wrote

A single sample? No. Multiple samples? It depends. When dosed, the concentration in blood rises for a period and then declines as it is metabolized and cleared from the body. Each drug has a sort characteristic curve for the drug and it’s metabolites that you could compare to a series of samples taken over time which you may be able to use to determine the initial dose. It depends a bit on the dynamics of the drug clearance, and at what times you took the samples.

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SwagarTheHorrible t1_j6go026 wrote

This. Also it would help a lot to know when the dose was taken. Lots of things once they've entered the blood stream are metabolized with sort of a half life. For caffeine, for example, it's about 5.5 hours. If someone has 100mg of caffeine in their system it could be because of the cup of tea they had in the last hour, or the cup of coffee they had six hours ago.

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SeeNoKarma t1_j6hlxou wrote

We do this with Wellbutrin in correctional psychiatry. Inmates will sometimes try to abuse this medication to get high (crush, snort, take more than prescribed), and they can also have it stolen or trade it with other inmates. With a random blood draw and a (supposed) time of last administration we can look at the concentrations of both the drug and its metabolite; their ratios give us an accurate picture of what the inmate has taken for the past three days.

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