How to compare the slopes of two graphs or trend lines

#1
Hi

I have 2 variables which trend over time ( by year). One variable is the mutation rate and the other is drug use. There are 333 samples each with a sample specific mutation rate while drugs use is a single variable over the entire year. For e.g.
ID year rate
1 2007 3.2 drug use 2007 = 10.4
2 2008 1.2 drug use 2008 = 4.5
3 2007 2.1
etc
I have been able to graph these (See attached graph), red = mutation and blue = drug use. Trend lines in black for each variable.

I would like to find out whether annual drug use impacts on mutation rate (which it seems to do) and if this is significant.

Could I ask what the best test would be to do this? (I have access to SPSS).

Thanks for the help
Sebastian