It has been used a hell of a lot as a PED, as as such is on the list of banned substances.
However it is addictive, highly catabolic, can lead to drug induced psychosis in certain people, will need increasingly larger doses to give the same effect and is dangerously euphoric which is related to the increased danger for addiction.
I have not used Speed in low doses, but have used it and used it a-plenty. I would not touch it with yours these days, and do not consider it worthwhile to any serious trainee.
The point is, if you are wanting more muscle, speed will not assist with this. Any performance increase it gives (and i am not denying this), it will counter any muscle gains with the catabolism it increases (stress hormones).
I have heard in it’s use during endurance events rather than anything needing strength and power, but i am sure the adrenaline release is useful for strength, although not in the long term.
Amphetamines used for endurancehis often also leads to dehydration issues and heart palpitations also.
It is a performance enhancer but is not a healthy drug, even in relatively small doses (for eg. if 1g is used to ‘party’ then a PED dose may be 1-200mg) IMO.
Even ephedrine - which feels just like a non-euphoric, bad speed - is highly addictive to many people, and they are using it for the same benefits you are looking for.
Add even more fat loss results, even more (perceived but not actual) clarity of mind, and even more euphoria, and you have a car crash waiting to happen.
I would add, IF one was to use this as a PED - it would be used during a competitive event, not for training, and most certainly not weekly!
If you want to do rec. drugs, fine… but don’t convince yourself you are doing it for muscle, performance or health.
JMO…