Risk Ratio help

Hey guys,

i am new to statistics and have a problem I dont know how to solve the best. So i analyze mutiple studies about two medications x and y, which is more effective. The outcome is, if event z does happen, so I choose to do a risk ratio with the program revman 5.

Now to my problem. Not all studies do compare both medications, some do compare only x with placebo and some do compare medcation y with placebo, but all analyze if event z happens.

If want to know, how i can leave a side blank. I can only insert 0s, but that ruins the data.

My approach was to do 3 risk ratios. 1 with medication x vs placebo, 1 with medication y with placebo and then just do a third risk ratio with the added together data.

Would appreciate any help, thanks so much