Sadly withdrawal from a lot of things can kill in extreme cases...but there's no real difference. The body becomes dependent on the substance to function. Medically assisted withdrawal is the safest for both alcohol and opiates. You can "power through" opiate withdrawal too, but it's pretty brutal...alcohol withdrawal actually may be "more dangerous" and likely to kill. The body reacts severely because the chemical processes in the brain are being disrupted; alcohol, heroin, and others interfere with the GABA receptors in the brain. The GABA system is the body’s main down regulator, and withdrawal causes it to go crazy.