Opioids that bind to certain receptors in the brain and activate them are referred to as “agonist” drugs (such as heroin and methadone), and those that bind to receptors but do not activate them are called “antagonists” (such as naloxone and naltrexone). Partial agonists (buprenorphine) bind to the same receptors but have less of an activation effect.

 Opioid agonist drugs have a range of pharmacological actions such as:

  • analgesia (particularly for relieving the affective component of pain)
  • a sense of well-being (euphoria)
  • sedation
  • central nervous system depression, particularly respiratory depression (in high doses)
  • pupil constriction

 The use of opioids can also produce side effects such as:

  • nausea and vomiting
  • constipation
  • increased sweating
  • decreased sexual function (impotence).


The onset of Heroin withdrawal may start as early as 4 hours after the last dose and reach a peak at 28-48 hours. The worst withdrawals are usually over by the 4th day and withdrawal usually resolves after 5-10 days. Some symptoms of withdrawal are more unpleasant than others. Hanging out is never easy and craving for the drug does not mean that you have to have the drug. 

Withdrawal from a long-acting opioid such as methadone usually commences 36–48 hours after the last dose. The peak severity of withdrawal tends to be lower than for

Heroin withdrawal, but withdrawal may be more prolonged, lasting 3–6 weeks.

The symptoms and signs of withdrawal from Buprenorphine are similar to those found in withdrawal from other opioids, but withdrawal from buprenorphine is generally milder than withdrawal from methadone or heroin because of its slow dissociation from the brains opiate receptors.

Symptoms commence generally within 3–5 days of the last dose and can last for several weeks.

Listed below are some of the symptoms you may or may not experience when you are withdrawing.  Some feel worse than others – following acute withdrawal, you may experience low grade symptoms of discomfort, both physical and psychological which may last for many months - all of them will pass in time.

This drug group includes –

Heroin, Methadone, Oxycontin, Endone and over the counter medications with a Codeine content.