That's true. I'll amend my statement: the law forbids harmful (eg lethal) medicine, not just harmful side effects. A deliberately lethal medicine is simply a poison. The law forbids both killing and suicide, so deliberate poisons are obviously illegal.
I'm not saying this is a good state of things; just that there's no hope of it changing. People will not be allowed to buy euthanasia drugs without a doctor's approval, because it will be seen as legalizing both suicide and poison that could be used to murder someone.
A deliberately lethal medicine is simply a poison.
The dose makes the poison and that has been known for ages. You can kill a man with water.
"Euthanasia drugs" only make death pleasant and painless. Often they are just an overdose of opiates.
Over at Scott Adams' Blog you can find a very fine example of using the 'Rationality Engine' to solve the social problem of assisted dying.