Service Directory for Drug and Alcohol Users


using opiates, drug half life and combining drugs

The half life of a drug is the amount of time it takes for your body to eliminate half of the initial dose.

For example, Valium has a half life of 20-40 hours (depending on how regularly you take it). What this means is that if you take 10 x 5mg tablets (50mg of Valium) at 3 pm, then by 3 pm the next day you will still have 5 tablets (25mg) of active Valium in your system. You may not still feel the same effect from the tablets you took yesterday, but they are still active inside your body.

It is always worth asking your doctor what the half life is of any medication you take. This includes methadone, anti-depressants and benzos especially. Information about half life is usually included in the pamphlet that comes with prescription medicines.

The most dangerous drugs to combine are called 'depressants'. These drugs depress your central nervous system (CNS), in other words they slow down your breathing and can even stop you breathing completely if you take enough at once, or even over a period of time. Heroin and methadone are CNS depressants; so are valium, alcohol, rohypnols and serapax etc.

When CNS depressants are used together the result is a drug combination greater than the sum of the individual drugs. The depressant effects are multiplied, into a very dangerous cocktail which could easily kill. It is especially dangerous to mix any CNS depressants with GHB.

If you are not sure which drugs are depressants check the 'Drug Reference Guide' in section 1, How Drugs Affect You, for more information.

You need to be particularly careful of drugs with a long half life. The figures given below are based on information on overdose prevention from HRVic and Moreland Hall. They are only provided as a guide, because the half life of a drug will vary in different situations (for example, according to how often you use it). This is why the half-life figure is usually stated as a range, as for Valium above (20-40 hours).

 
Drug type Name Half life (hours)
Benzos: Mogadon (nitrazepam) 26
  Serepax (oxazepam) 5-15
  Valium (diazepam) 20-40
  Rohypnol (flunitrazepam) 25
  Normison (temazepam) 18-30
  Rivitrol (clonazepam) 20-60
  Frisium (clobazepam) 18
  Euhypnos (temazepam) 10-15
  Tranxene (clorazapate) 2
Opiates: Methadone 15-32
  Heroin 8-12
  Temgesic (low dose buprenorphine) 1.2-7.5
  Morphine 3
Anti-depressants: Tryptanol/Endep (amitrityline) 12-36
  Deptran (doxepin) 17
  Prozac (fluoxetine) 60
  Tolvon (mianserin) 33
  Nardil/Parnate (phenelzine) 2
  Zoloft (sertraline) 26


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