Higher productivity through Stimulants

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Aside from the use of stimulants to induce euphoria, stimulants are widely used to increase productivity. This is functional use of stimulants.

In contrast to the use of stimulants to induce euphoria, several aspects of stimulant use are highly unwanted:
Side effects interfering with concentration, motoric function or normal appearance. Overstimulation is also highly unwanted.
Where in the case of the use of stimulants to induce euphoria, a user may feel that substance specific side effects are part of the game, these side effects are absolutely not done in the case of functional use of stimulants.

There are many stimulants used to increase higher productivity. Ranging from the well known caffeine and amphetamine to lesser known drugs like MDPV.
Many pose high risk to addiction or health.

Please post which stimulants SWIY tried and how suited you rate them to induce productivity. Please note dose, pro's and cons and explanation.
Which stimulants did SWIY find not suited for functional use?
If SWIY has found SWIY's optimal stimulant, please explain why.

The main goal of this tread is to get a complete overview of stimulants as functional tools and their effectiveness as such.