Consider half life during drug detoxification

A young man on my sobriety-based detox program (only after showing positive for opiates) admitted to heroin-usage, but hedged the matter saying it was “5 days ago.” His implicit presumption was that an isolated episode, days ago — compared to continuous, more recent, heroin-usage — would lessen the likelihood of his getting kicked off the program.

Is his story of “no heroin [ingestion] in the last five days,” likely, the whole truth? The half-life of heroin, itself, is only a few minutes; however, it metabolizes directly into similarly narcotic morphine, whose half-life is a matter of a few hours.

Do patients understand the concept of “half-life”? I explained (in a simpler fashion than the terms imply) the inverse exponential nature of the decay curve, i.e. that if morphine’s half-life is (to be very generous with him) six hours, then the “quarter life” is 12 hours; only 1/8 remains after 18 hours, and only 1/16 after one full day. After five full days, there would be 1/16*1/16*1/16*1/16*1/16, or around one one-millionth (!) of the original heroin-equivalent left, way beyond the sensitivity of qualitative drug-testing. In this young healthy man, morphine’s half-life more likely is only three hours, thus after five days, only one millionth of that one millionth, i.e. 1/1000000000000 remains.


Most of my narcotic addicts have adequate and pragmatic math skills, in so far as knowing how to get enough money to feed a drug habit, but explaining a decay curve might be fruitless. I tried flipping the concept around and that seemed more understandable: asking how often, when fully addicted, he would have to take heroin. “Four or five times per day” was the answer. “Why four or five times per day?” I asked. “Because after a few hours, withdrawal-symptoms kick in.”

“Well, there’s your half-life! If heroin lasted four days and could be hanging around as morphine days later, you wouldn’t need to be taking it every few hours, you would take every few days”, I responded. And the point was made.

The same goes for marijuana, THC, albeit on a slower decay curve basis. My addicts (in a self-serving manner) always tell me that they “know” that marijuana hangs around for a month and will show positive for a month. They have that information on word-of-mouth. Certainly, on the outside, with high body fat content and high marijuana-usage level, marijuana (with a half-life of approximately 30 hours) will stay around longer; however, in actuality ~80% of my patients have it out of their system, according to qualitative testing, within about 5-7 days of beginning our sobriety program. Closer scrutiny and questioning almost always reveals that those with persistent positive testing of marijuana have had a few “lapses” using marijuana in the interim.

These are important points to emphasize during a detoxification, to stay on top of some of the ready-made excuses that narcotic addicts are very used to bringing up to avoid and evade closer scrutiny and full sobriety; often obtaining replacement-narcotic while indulging, still, in the “drug-life.” If a treatment professional is going to indulge these excuses, do so with eyes wide open, but invite even more testing of boundaries.

Randall S. Bock is a primary care physician who blogs at Withdraw to Freedom.

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