Does caffeine (100-120 milligrams) inhibits protein synthesis completely? i only have one strong coffee a day,morning or before lifting weights.

Performance enhancer: I am unaware of caffeine inhibiting protein synthesis in any meaningful way. Multiple studies and thousands of years of practical use have demonstrated that caffeine is a great athletic and mental performance enhancer.

NO: Caffeine's primary mode of action is to accelerate release of glucose into the bloodstream from its storage form called glycogen which is contained in muscle to provide fuel during the initial anaerobic phase of muscle activity. As glycogen stores are depleted we switch to oxygen for fuel. Replacing glycogen stores might temporarily supercede protein synthesis but the effect would be negligible.