If you feel that the only way you can achieve what you want is to take amphetamines then I would hope that what you are working on is very important (for you at least). The side effect from overuse are enough to take years off your life.

Also I suspect that no doctor would willingly supply you with amphetamines just so you can work harder. Doctors write prescriptions for medical conditions and not life style.

Ask yourself how long this difficult work can be expected to last, if it is essentially your job then you'll probably have to take amphetamines for as long as you have the job.

Paul Erdős only gave up for a month so I suppose we can call him an addict. And you are no Paul Erdős.