I have been given a prescription for cimetidine syrup.

You could use the following compound for a beverage, which contains 200 mg cimetidine per 5 ml. We Prepare 100 ml of oral solution, which corresponds to 4 G cimetidine

R/Cimetidine 4 G, HCL 1 M 16 ml, water 24 ml and sorbitols syrup not crystalizable to 100 ml.  

If necessary, a taste corrigens can be added.