How do drugs affect the central nervous system?
Different Drugs have different effects on the Nervous System..
But to keep things simple, Our brain regulates different chemicals to function like neurotransmitters, hormones, enzymes, amino acids and many more.
Some drugs imitate how this chemical function, some drugs change how this chemicals function, some drugs prevent this chemicals to function, some drugs speeds up this chemicals to function and All drugs will alter your perception and emotion(You become hyper, down, tired, nervous, relax, sad, happy, high and many more)
It's just basic chemistry, Chemical change and Chemical reaction. When you mix, remove or replace chemicals, there will always be an effect.