What are the long term side effects of methadone? what about suboxone?

They vary: Methadone has very few organ-specific toxicities. Constipation, weight gain and edema are the most common. In very rare cases, it can cause a heart arrhythmia, but this effect is temporary. It can lower male hormone levels. Physical dependency and the need to very gradually taper the medication is the most specific side effect. Buprenorphine also causes constipation and low testosterone.

Some good ones: Methadone can lead to sudden cardiac death at high doses, half life is not as predictable, can have many drug-drug interactions. Suboxone is considered safer. If doing a risk-to-benefit analysis & the choices are staying on illicits or suboxone, the latter wins. Side effects are outweighed by its benefits in many individuals. The 10 year experience in usa limits the answer to 10 years.