Elimination half-life

The “elimination half-life” is the time period it takes for the plasma concentration of a drug to be halved. Hence, each successive half-life, less drug is eliminated. After one half-life the amount of drug remaining in the body is 50%, and after two half-lives 25%, and so on and so on.

In other words, if you shoot 10mg of heroin at 1:00 pm and at 1:05 pm there is only 5mg of heroin circulating in your system, you would say that heroin has a 5 minute elimination half-life. Ironically, heroin’s elimination half-life is 5 minutes. Some scientific research says it’s actually less than 1 minute, but only when heroin is injected.
 

Heroin’s half-life

Heroin will metabolize in half and into 6-monoacetylmorphine (6MAM) in about 1 to 5 minutes. 6MAM will metabolize in half and into Morphine in about 6-25 minutes. When people use heroin, it’s actually a combination of these 3 drugs that intoxicate users. For this reason, the elimination half-life of heroin is considered to be a combination of these three half-lives; heroin (less than 5 minutes), 6MAM (6 – 25 minutes) and Morphine (2.5 – 5 hours).

The elimination half-life of heroin is therefore 2.68 to 5.5 hours. Secondly, the drug effects of heroin generally last between 1 and 2 half-lives. Following the logic, the effects of heroin range between 2.68 to 11 hours. In other words, the effects of heroin last, on average, about 6.84 hours, which is the midpoint between 2.68 and 11.

 

The Math

If you look below you’ll see a bunch of numbers listed 1-8. Number one represents 1 half-life, or 50% (1/2) of the original amount. Number 7 represents 7 half-lives. The product of number 7 is 1/128, which means less than 1% (.78%). Since it takes 7 half-lives to get below 1% of the original amount, it’s safe to say, that heroin is effectively gone from your system between 7 and 8 half-lives.

  1. 1/2 or 50%
  2. 1/2 x 1/2 = 1/4 or 25%
  3. 1/2 x 1/4 = 1/8 or 12.5%
  4. 1/2 x 1/8 = 1/16 or 6.25%
  5. 1/2 x 1/16 = 1/32 or 3.125%
  6. 1/2 x 1/32 = 1/64 or 1.562%
  7. 1/2 x 1/64 = 1/128 or .78%
  8. 1/2 x 1/128 = 1/256 or .359%

 

The Conclusion

The half-life of heroin is at most 5.5 hours, i.e. 5 minutes for heroin, plus 25 minutes for 6MAM, plus 5 hours for Morphine. If you multiply 5.5 by 8 (for 8 half-lives), you come up with 44.0 hours, which is when heroin withdrawal generally peaks, though its symptoms generally plateau for almost 24 hours. That is why heroin withdrawal is most difficult between the second and third day.