A substance made up of about 60% amphetamine.
In contrast to speed
, which is made up of about 5% amphetamine.
Often methamphetamine is defined as base: "a purer form of speed".
Methamphetamine is a completely different chemical, with different effects. Base is the same chemical as speed, just in much higher concentrations.
Usually has a different effect to speed, as the higher dosage doesn't just mean fuller effects, but whole new ones as well.
NB: both amphetamine and methamphetamine have absolutely NOTHING to do with 2,3 methylenedioxymethamphetamine (ecstasy), despite the uneducated and ill-informed ramblings of the DEA.