You'd have to calculate the load of the circuit to determine if you have enough capacity.
Volts x Amps = Watts
So if you are in the US, you probably have a 15 amp circuit which should only be loaded up to 12 amps. Now go add up everything else on that circuit. Lets say you have 10 pot lights at 50watts each.
120v x Yamps = 500watts
Now lets say your two lights are 100W each, that's another 1.67 amps (200W/120V), so 5.7 amps total being drawn which means you would be able to add these without overloading the circuit.
If the circuit was already approaching 12amps, you would not have enough capacity and would need to run a new circuit.