Because your body has developed a tolerance to methadone (page 8) it may react or withdraw when the level of methadone in your system drops below a certain level,

Every part of you that is affected by the methadone becomes geared up to function with the drug inside you, so if you stop taking methadone your body takes time to adjust to not having it there. During that time you may suffer withdrawal symptoms such as

A high temperature but feeling cold, with goosebumps alternating with sweating

Feeling restless, anxious and aggressive

jerking arms and legs

Disturbed sleep

Diarrhoea

Feeling or being sick

Running eyes and nose

Pains in muscles, bones and joints

Yawning and sneezing.

But too much methadone can cause sweating, feeling sick and poor sleep too, so you may get these symptoms - which feel like withdrawals - at the start of a script or if you change from taking your methadone several times a day to once a day.

Because methadone is a longer-acting drug, some people find the withdrawals more uncomfortable and longer lasting than with heroin. But once it is out of your system the mechanism of readjustment is the same whether you've stopped methadone or any other opiate.

Withdrawal symptoms are probably due to oversecretion of noradrenaline (production of which is suppressed by opiates) and partly because methadone has reduced the secretion of the body's natural opiates called endorphins. Following the burst of noradrenaline your body may be short for up to eight months. This may be partly why people still feel anxious, cold and/or have difficulty sleeping for months after stopping a script.