Methadone Side Effects

Methadone's side effects are similar to those caused by morphine, including lightheadedness, dizziness, drowziness, mental clouding, sweating, pruritus, nausea, and vomiting. As with morphine and meperidine, the side-effects more frequently occur after oral than after parenteral administration, and more often in ambulatory than in bed patients. The principal danger of overdosage is diminished pulmonary ventilation.

Observations from the Philadelphia programme indicate that about 15% of the addict-patients develop minor side-effects from using methadone HCl. Among those side-effects observed were constipation, delayed menses, obesity, ankle oedema, occasional nausea, and impotence in males. Constipation is the most common side-effect observed. Several investigators reported sexual impotence in at least 25 % of the males studied in other methadone maintenance programmes around the country. The incidence of sexual impotence reported in the Philadelphia programme was around 10%.

In assessing the abuse liability of methadone and its cogeners in man, volunteer post-addicts who received subcutaneous methadone four times daily developed tolerance to the analgesic, nauseant, myotic, sedative, respiratory depressant, and cardio-vascular effects; tolerance to the constipating effect was not developed. Although tolerance to methadone develops more slowly than to morphine, especially with respect to the depressant effects, this may be related not so much to slow development of tolerance as to the cumulative effects of the drug. Marked sedation, with concommitant slowing of the EEG occurs during the first few days of experimental addiction, and the behaviour of the methadone addict is strikingly similar to that of the morphine addict.

Development of physical dependence upon the chronic administration of methadone can be demonstrated by drug withdrawal or by administration of the narcotic antagonist nalorphine. Subcutaneous administration of 10 to 20 mg of methadone in former narcotic addicts produces definite euphoria, persisting somewhat longer than that caused by morphine. As with other drugs, methadone has become a source of potential abuse, and many addicts now prefer the effects of the synthetic compound to those of the natural alkaloids. The over-all abuse incidence of methadone would seem to be somewhat lower at this point than that of morphine, but increasing numbers of addicts have added methadone to their list of abused drugs.

Methadone side effects include but are not limited to:

• drowsiness
• lightheadedness
• weakness
• euphoria
• dry mouth
• urinary retention
• constipation
• slow or troubled breathing

Methadone side effects that are more rare include but are not limited to:

• allergic reactions
• skin rash
• hives
• itching
• headache
• dizziness
• impaired concentration
• sensation of drunkenness
• confusion
• depression
• blurred or double vision
• facial flushing
• sweating
• heart palpitation
• nausea
• vomiting

Methadone side effects that are more uncommon include but are not limited to:

• anaphylactic reactions
• hypotension causing weakness and fainting
• disorientation
• hallucinations
• unstable gait
• tremor
• muscle twitching
• myasthenia gravis
• kidney failure
• seizures