The effects are not explicitly stated in the Netflix series, but to lift a few quotes from the books:
In The Witcher, he consumes two potions:
The mixture which helped the witcher gain full control of his body was chiefly made up of veratrum, stramonium, hawthorn and spurge.
The other ingredients had no name in any human language. For anyone who was not, like Geralt, inured to it from childhood, it would have been lethal poison.
In the silence his hearing, sharpened beyond measure, easily picked out a rustle of footsteps through the courtyard overgrown with stinging nettles.
After drinking a mixture of banewart, monk's hood and eyebright the face takes on the colour of chalk, and the pupils fill the entire iris. But the mixture enables one to see in the deepest darkness...
He did not want the magnate to realise how fast his movements and reactions now were.
These effects are described again in the second short story:
You're sick, Geralt. You react to elixirs badly. You've got a rapid pulse rate, the dilation of your eyes is slow, your reactions are delayed. You can't get the simplest Signs right.
- The Voice of Reason, The Last Wish
In the second book, we are told:
After the elixirs you wouldn't even have felt an open fracture, until the protruding bones started snagging on hedges.
- The Sword of Destiny, Chapter 3