Methadone is the generic name of the chemical itself there are brands of methadone out there such as dolophine and methadose.
Methadone hydrochloride is chemically described as
6-(dimethylamino)-4,4- diphenyl-3-hepatanone hydrochloride.
The hydrochloride salt form of methadone is what's commonly used and is mainly used in the treatment of opioid/opiate addiction. It is not quite synthetic heroin per say but the poster above is right in saying the effects are quite similar. Because it is an acyclic analog of morphine or heroin, methadone acts on the same opioid receptors as these drugs, therefore it has many of the same effects. Methadone was created in Germany in 1937 because opium trade was falling through due to the war so people in pain needed a reliable source of opiates. Methadone is a synthetic drug that could be made with readily available ingredients solving Germany's opium shortage problem.
Germany stopped using it when soldiers reported side effects such as lethargy and 'an unwillingness to go to battle" to quote Germany.
Methadone is also used in managing severe chronic pain and Is quite effective with a long duration of action, strong analgesic effect, and very low cost. It seems to work very well with nerve pain and can be considered one of the strongest opioid type drug available for pain. When other opioids fail, chronic pain patients can usually find relief with methadone.
If you have only done weaker opiates such as hydrocodone and oxycodone then be very careful with methadone. It doesn't carry quite the same euphoria as other opiates even in high doses but it doesn't mean it isn't working so don't keep taking more to achieve the same "high'' you are used to or you may have breathing problems. Start with 5-10 mgs of methadone then wait 3 hours see how it effects you then take more if desired. Methadone takes a long time to peak so don't keep popping them every half hour thinking its not working because it can take 3 hours to fully peak. In general the conversion would be for every 3mg of methadone the equivalent dosage of oxycodone would be 5mg.
Because of its long half life and duration of action methadone is great for stabilising heroin addicts as a "matinence" medication. Instead of a heroin addict dosing 4-6 times a day they can usually get by with one dose a day when on legally prescribed methadone and it keeps them from having to resort to crime to get their fix therefore taking the strain off our prison system,lowering crime rate, etc.
It also makes an opiate taper alot easier due to its long half life since short acting opiates are so hard to taper down due to the amount of times redosing is required. Many heroin addicts switch to methadone to either stay on indefinitely or to taper down over the course of a couple months or more. Its usually given out to them one dose a day so they have to go to a clinic and dose in front of a pharmacist each morning to avoid misuse of the methadone.