This is the first time i encounter this kind of word "Methadone", I don't know what this really means and according to the wikipedia methadone is actually a medicine.
Heres the definition and adverse effect of this medicine from wikipedia.

Methadone such as Symoron, Dolophine, Amidone, Methadose, Physeptone, Heptadon and many others, is a synthetic opioid, used medically as an analgesic, antitussive and a maintenance anti-addictive for use in patients on opioids.

Adverse effects of methadone includes;

* hypoventilation
* decreased bowel motility - constipation
* miotic pupils
* nausea
* hypotension
* hallucination
* headache
* vomiting
* cardiac arrhythmia
* anorexia (symptom)
* weight gain
* stomach pain
* xerostomia
* perspiration
* flushing
* itching
* difficulty urinating
* swelling of the hands, arms, feet, and legs
* mood changes
* blurred vision
* insomnia
* impotence
* skin rash
* seizures
* death