What ssri between lexapro (escitalopram) and prozac work better to treat depression, ocd, and anxiety? which is known to be a more effective drug with no weight gain

Both equal: Both are good choices. Portion control and Exercise should limit weight gain.

Personal chemistry: It really depends on your personal chemistry. Different people react differently to each medication. There are some common side effects (like weight gain) but those only happen in a percentage of the population. Work with your Dr to find which medication is a best fit for you.